When Bryan Fuller started this and it was basically just him and his staff figuring out ideas, it wasn't an always prequel, it was an anthology series that would jump around into eras of Trek we hadn't seen. Then Kurtzman and the rest got involved as he was bailing and it became Orci and Kurtzman's third movie pitch, a war against the Klingons. I'm pretty sure that's why Fuller ditched on the series as he didn't want to fight them over the prequel aspect and saw how it could still work before he realized they had shuffled him aside.
A prequel CAN work because there is a huge gap in the Trek timeline that is full of named events which don't have any fleshed out details but could be dramatic and interesting. The Tomed Incident for example is what took the Romulans from a powerful player in regional politics to shutting themselves up on the other side of the Neutral Zone until TNG, this is arguably the biggest untouched event in Trek lore since it made an entire Star Empire go hide for 80 years without the most powerful two neighbors knowing shit. The Enterprise-C's sacrifice at Khitomer (a last gasp of the Romulan Empire perhaps?) and the Federation-Cardassian War are two periods that leave the status quo we got for TNG and into DS9. There's also a war with the Tholians at some point. And some others, they're all mentioned as recent enough for TNG/DS9 crew to have experienced them.
And this makes sense if you take the Alpha Quadrant as we know it as TOS films end and TNG starts. In TOS the Romulans and Klingons were still far away and only at the end of TOS and in the movies did the Klingons start encroaching and battling with the Federation seriously over territory. While the Romulans had signed an alliance with the Klingons that at some point fell apart to such a disaster that they tried to wipe out the Klingons before hiding for 80 years. The Federation had expanded by the time TNG starts to reach Ferengi, Breen and Cardassian space. Which is opposite the Klingon and Romulan Empires on the maps.
Even though there's obvious parallels for the way the races act, if you take what Trek presents in terms of distance, the TOS takes place in Continential Europe, and TNG has them reaching quite deeply into Africa, Russia, the Middle East, etc. The Americas are the Delta and Gamma Quadrants. Or maybe the Americas are the Delta Quadrant and Far Asia is the Gamma Quadrant.
So that whole period between VI and TNG has the Federation expanding and expanding and causing tons of known conflicts with brand new races they're meeting. The seeming sudden collapse of one Empire and meeting another powerful one which a major war is fought with. Along with smaller events that are all termed wars by people who served. While the Klingon Empire is rebuilding from the events of VI, which the film speculates will take them decades. So the Federation was basically unchecked by the original TOS powers during this period except the Tholian War whatever that was.
Except they want to do prequels pre-Kirk for whatever reason. It would have worked with
Enterprise but they got cold feet about limiting the scope of the ships travels, wasted so much time on the time travel bullshit and introduced the Xindi for no obvious reason when they had tons of races to use, namely the Romulans, and they had ideally setup the series as building to and ending with the Romulan War (which is a canon snarl) and the founding of the Federation. If the Xindi attack in season three is unknown, but the Enterprise heads out there to find out who's behind it and we get the first inklings of it being the Romulans, then season four introduces the Romulans as it did and also brings about the Vulcan Civil War as it did along with the first real teaming up of the founding Federation races, the show is using its most powerful thematic arcs to setup the conclusion of the series. They couldn't write this way because they rebooted the show twice instead. Then spent half their bonus season on AUGMENTS and then KLINGON AUGMENTS to explain away the forehead ridges rather than take what Jack noted was a potential storyline in the human/Earth backlash against aliens, especially after the Romulan attack ("unknown" still except to the viewer and maybe the Vulcans and maybe Archer finds out at the end of the storyline) and the Vulcan's constant bullshit for years.
Discovery makes zero sense taking place in the ten years before TOS, which we've already seen! The Cage! And TOS never indicated there was a major war with the Klingons that reshaped their entire society, only the Romulans. That's why the crew knows how to handle the Klingons in every episode they meet up, even has half-friendly ones like Tribbles, but the Romulan episodes are cloaked in guessing and spycraft. It suggested the Klingons as a race the Federation had scuffles with, but were generally handled, while the Romulans were an open-ended threat. The first episode we meet with the Klingons (Errand of Mercy) is setup with the premise that things have gotten so bad recently that they may have to actually go to war with the Klingons but in the end even with it forced on them they sign a peace treaty, which holds. Never again are the two at open war until DS9. Every instance of skirmish is either a setup ("Day of the Dove") or a rogue Klingon (III, V and VI...with Klaa notably being chastised for attacking the Enterprise for his own ends and VI being an outright conspiracy between all kinds of forces...III also was originally supposed to be the Romulans going after Genesis) compare to the Romulans or even the Gorn or Tholians who are never nothing but hostile and on the verge of total war with the Federation. With the Romulans backing down regularly, especially in TNG, because they're constantly probing rather than looking for an actual war.
Fuller's original pitch would have worked far better in terms of being what Trek needs in terms of a show that's full of familiar stuff, a show that has seralized seasons and a show that can also try new things for Trek.
When Fuller first met with CBS about the series, the company did not have a plan for what the new show would be. He proposed an anthology series with each season being a standalone, serialized show set in a different era, beginning with a prequel to the original series, then stories set during the original series, during Star Trek: The Next Generation, and then "beyond to a time in Trek that's never been seen before". Fuller compared this to what American Horror Story did for horror, and described the proposal as a platform for "a universe of Trek shows". However, CBS told Fuller to just start with a single serialized show and see how that performs first, and he began further developing the concept of a prequel to the original series.
This would have allowed you to do something like say a season where the Federation first meets the Cardassians, who are arguably the most un-Federation/human like race, and it descends into war. Throw in some mentions about a Chief O'Brien or even cast somebody to be a young him and that's all the connections you need, the rest you can do all new, get your war story (one which clearly was intense enough that it affected people we saw on TNG) and shit.
They could setup seasons based around where TNG/DS9 only spent a few episodes, the contingency side of the Federation. Especially in the wake of the Romulans reappearance in TNG. ESPECIALLY in the wake of the Borg attack and then the discovery of the Dominion. Section 31 operations paired with a ship that has plausible deniability but the captain is unsure about this all, and they could have the debate DS9 never let them (because they were bringing the series arc to a close) regarding how much of this is shattering Federation ideals. And how much has been how the Federation has always operated.
What about seasons where we go back to all those places the Enterprise fucked up and then warped away from? We constantly heard about how this or that race was applying for the Federation but then we'd find out their SECRET and Picard would lecture them and warp away. There's all sorts of stuff on both ends of that happening. Especially when they reveal themselves to lesser races and Picard becomes a god or whatever. Set a season around the people who have to clean up those messes or go through all the setup and planning. Even when they got a movie to do this with they fucked it up. If you take what we know from
Insurrection it's clear it's not the first time the Federation has relocated races. Explore that.
You can do all of this in prequels. It's arguably the easier way to do it and better way,
Enterprise originally set its first season date so it would be hemmed in by the Romulan War and Founding of the Federation which were two set in stone Trek dates. Only they had no idea how to fill the time to get there and were clearly not interested in really exploring the simplicity of the concept or the notions of exploring and first contacts. Thus why we have Klingons in the first episode plus the announcement of a massive TEMPORAL COLD WAR THAT WILL CHANGE EVERYTHING AND IS THE MOST IMPORTANT oh never mind look they're space Nazi's bye.
Kurtzman later added that the Federation-Klingon War story arc of the first season would not continue in a second season, saying "each season needs to be about a different thing".[78] However, he was not interested in a full anthology series because "I wouldn't necessarily want to throw [the characters] away at the end of the season for a new show",[79] and instead felt that the aftereffects of the first season would be felt moving forward: "The results of the war are going to allow for a lot of new storytelling that will be the result of everything that happens and the people that are left behind; the casualties, the things that have grown in Starfleet as a result of the war. That's what we'll inherit in the second season."
By the end of August, Berg and Harberts had developed a "road map" for a second season, and "the beginnings of one" for a third. It was also revealed that an average episode of the first season had ultimately cost US$8–8.5 million, making it one of the most expensive series ever alongside successful shows like Game of Thrones and Westworld, but also infamous failures such as Marco Polo and The Get Down. This increase in budget outgrew the original Netflix deal, but CBS still considered the series to be paid for already due to the number of new All Access subscribers that the show was expected to draw.
"The defining factor of Roddenberry's vision is the optimistic view of the future ... Once you lose that, you lose the essence of what Star Trek is. That being said…we live in very different times. Every day we look at the news and it is hard. It is hard to see what we see. I think now more than ever Trek is needed as a reminder of what we can be and the best of who we can be. Star Trek has always been a mirror to the time it reflected and [the topical question now] is how do you preserve and protect what Starfleet is in the weight of a challenge like war and the things that have to be done in war. [That] is a very interesting and dramatic problem."
—Executive producer Alex Kurtzman on the balance between classic Star Trek and new elements in Discovery