You didn't really dig deep.
It's oddly a point I was going to make about PD's Hogger example. He was willing to learn what to do and try crazy stuff because it was his first MMO and for some reason people at the time more willing or accepting of a challenge they may not understand.
That's what people encounter when they face something in which they expect the trinity but it's not there. I died and ran back a lot on my first dungeon as well. Then I learned the dungeon and learned more about the combat. The difficulty jump between open world leveling fights and dungeon encounters is rather steep. And the difficulty and concept demand between dungeons and Fractal dungeons is large as well. The issue is people playing these systems while thinking in the manner of older systems. If the trinity is not there then you shouldn't expect to be able to know what to do and not expect to operate like you do in a common trinity system. Some people adapted and others did not.
Those that did not adapt often accuse the game of being chaos. You can level to 80 by being spammy and avoiding the more difficult stuff. It seems a lot of people have done so. When they added a daily accomplishment for dodging, people were asking how to dodge in level 80 areas. That's kind of amazing considering it's an important part of the combat mechanics. However, people not looking for depth doesn't mean there isn't depth. There's a lot of depth and skill in the combat. How I played as a level 30 new player is very different than how I play now. Players seem to progress from spamming through chaos, to spamming and dodge out of chaos, to finally parsing the battlefield and putting to use everything they can. Then you realize that it's not "pure chaos", but just the fog of war. You learn to recognize skills, behaviors, combo fields and conditions. You learn the game. You learn the new non-trinity system.
The thing is that people don't seem to want to learn. People are willing to learn in their first MMO, but not in their third/fourth/tenth MMO. I have found that people who never play MMOs adapt to GW2 much better than the MMO vets. The Diku history of EQ and WoW have indoctrinated people to the point where it's very hard for them to recognize they're using a hammer when they should be using a fork, that they don't recognize possibilities, and don't give credit to their need to learn.
A criticism I would lob at the game is that it doesn't challenge players to learn the game often enough. Though when the game does challenge players, many scream chaos and spam and die. I am not sure how you solve that as a developer.* The weakest parts of dungeons is that many of the bosses have boring mechanics. Only the renovated Ascalon Catacombs and Fractals have some cool stuff. (With some exceptions to places like Sorrow's Embrace and Crucible of Eternity).
*I am pissed that they are nerfing the damage on the Confusion condition in WvWvW. For the non-GW2 players, Confusion is a debuff/condition that doesn't do damage over time, but instead does damage when the target uses a skill or ability. It stacks in intensity but doesn't last as long as most other conditions. There was no reason to nerf the damage on Confusion. I rarely suffer big spikes from Confusion in my time in WvWvW. I recognize the signs the confusion is coming via the giant pink circles from Mesmers, recognize when I have the condition on myself due to it making you have a pink glow around your body, and either cleanse the condition off of me or stop attacking for a couple of seconds and watch the condition fall off. It's being nerfed because bad players don't do anything but spam through Confusion and kill themselves. I know because I run a Glam Confusion mesmer in WvWvW and decimate loads of people who don't simply recognize what is going on and adapt. For fucks sake, there's a giant pink bubble and you're standing init and every arrow you shoot bounces off the bubble and back in your face, and you just triggered 5 stacks of confusion because you don't leave the giant pink bubble or cleanse yourself and voila you're dead by your own stupidity.
At some point you got to let players be punished for not learning the game.