The problem is that I think that whatever good Republicans can achieve by simply being opposition to Democrats will be undermined by Trumpism. The only person in the GOP with any kind of status who didn't knuckle under to Trump was Mitt Romney. Ted Cruz could have stood up for movement conservatives and the Evangelicals that made up his primary base and tried to frame an internal constraint on Trump, but instead he immediately kissed the ring. Paul Ryan and Mitch McConnell fell all over themselves to get Trump "wins" that went against years of conservative principles. Even in the case of judges, which was the most successful part of the four years of Trump, many of those appointed were simply shitbags with no experience rather than principled conservative judges or originalists or whatever else you'd expect. And this was all despite the fact that Trump didn't really care about any of the specifics in any of this. When they were trying to "repeal and replace" Obamacare some actual conservative opposition to the bill popped up and Trump told them he didn't care about "the little shit, only the big picture" and just wanted something, anything passed that would let him claim he repealed Obamacare and instituted a great superior Trumpcare. (And even at this, they failed.)
The reform plan the party was coalescing around after the 2012 results is dead except for the bad parts. Free trade? Out. Immigration reform? Instead we got zero tolerance, illegal bans, malicious prosecution and pursuit of "the wall" on the wrong border. Budget and debt controls? Gone, he surpassed even Bush on this front and Bush at least had the excuse of the wars he started. A truce on the culture wars? Instead the social moderate Trump did everything possible to amplify them and appointed plenty of fervent nutsos on this. (Although some of this has backfired, Goursch writing gender identity into anti-discrimination laws for example, ACB so far refusing to go along with Alito's social conservatism. Even if Dobbs is a "win" by upholding Mississippi's law, I don't think they're going to touch Roe/Casey. I could be wrong though!) Foreign policy? All over the place, some was actually good, most of it bad and counterproductive to stated goals, never ended the drone wars. Withdrawing from the Iran deal, setting up Afghanistan to fail, etc. Respect for the institutions and constitution? lol, to use just a single example, I'll point out that he targeted ACB as a traitor (to where she gets more death threats from Trumpists than Democrats still) just months after appointing her simply because she agreed with the law and precedent that the Supreme Court had no authority to intervene and overturn an election result in multiple states because Texas wanted it to.
I still don't think Trump is the worst President in history (I'm partial to Nixon) and as noted above I do think he did a few good things even if by accident but he was a unique aberration in terms of his political force. Nobody else can pick up his mantle and run with it. Nobody else can keep his unique base. The GOP is harming everything by continuing to be completely subservient to the man. Ryan and McConnell fucked up when they decided that was the "message" of 2016 but after 2020 and Jan 6th, the party had ample chance to challenge him and they mostly haven't.
It's early, but it's also funny, at the moment the only person it looks like can stand up to Trump is DeSantis. But he might actually be worse than another four years of Trump. Ideally, Trump stays out of 2024, doesn't endorse but also does turn on DeSantis and those two spend it fighting, opening a path for somebody more reasonable like Nikki Haley or Kristi Noem or Tim Scott, or god forbid, even Ted Cruz or Marco Rubio. That seems like the only likely prospect for the Republicans to come back from Trump at this point. I mean, other than him just keeling over sometime soon. But I imagine he'll be one of those types that just refuses to die despite so many reasons why he should. Like Strom Thurmond did.
Anti-Trump efforts that defect blindly to the Democrats (Lincoln Project, Jennifer Rubin) are useless. There needs to be strong anti-Trumpism within the Republican Party. But there isn't. Maybe something can center around Glenn Youngkin, if only to provide an outpost of opposition. But I thought the same about Ted Cruz and Rand Paul after 2016. Both became loyalists instead. (Rand was especially disappointing personally, and it's why I can't take him seriously on anything anymore.) Ryan and McConnell became loyalists. Kevin McCarthy ran to the front of the parade practically. Even Sarah Palin was more skeptical of Trump than these idiots.
The problem as it I see it is within what you note, the Republicans will gain simply because they're not Democrats. But that won't cast Trump out of control, if anything it may strengthen his hold. We'll have primaries where Trumpists win because he backs him, and then they go on to win general elections simply because they aren't Democrats. Trump will claim credit and victory and most of the party will continue to worship him despite the fact that it's not sustainable when he does leave the scene after 2024.
edit:
And Lee Zeldin, the Republican candidate for Governor, is a huge Trump bootlicker, antivaxxer, antimasker - just an all-around awful person, he's been my district rep for years now. Trust me, even with how awful the Dems have been, Zeldin is worse.
This is exactly the kind of thing I'm talking about. A socially moderate, reasonable conservative can win New York. Especially when Democrats suck. (And everything about Kathy Hochul indicates that she sucks.) That was George Pataki (and before him Nelson Rockefeller) for three terms! Rudy and Bloomberg did the same in NYC proper. There's similarly politically strong Republican Governors in deep blue Massachusetts and Maryland right now. But a Trumper can't do this. And right now, Republicans seem to accept only Trumpers.