When he chooses Palpatine, he’s making a deal with the devil to “save Padme’s life”, liberating himself from the [Jedi-informed] conscience he did have. It’s not that what he does from here “doesn’t count” but it’s not a reflection of who he is (well, idk, loaded philosophical question) or who he wants to be. Hayden crying is some of the most striking imagery in ROTS and it happens several times.
I think the problem with Anakin’s decision to follow Palpatine is the absurdly extreme cost of doing so that Anakin has to pay right up front. I mean, I can understand Anakin (or anybody, really) agreeing to do some seriously evil stuff in order to save the life of a loved one. But Anakin is told that, in order to save Padme, he has to basically mass-murder everyone he’s ever known, including children. That goes well beyond “my first Dark Side experience”. The justification, I guess, is that Anakin desperately wants to save Padme and he’s slightly pissed off at the Jedi for denying him a Council seat. But this is so weak - the character-work really isn’t there in the script to justify Anakin’s decision. It’s a ridiculous and jarring leap to go from “well I’m now an accessory to Mace Windu’s murder, I might as well just roll with the whole Dark Side thing” to “I will now methodically murder hundreds of people including defenseless children on the off-chance this Sith stuff pans out and saves Padme”.
I think it’s important that those upfront costs aren’t his First Dark Side Experience™. It’s still the Tuskens.
What I’m positing is that the guilt and self-hatred of that has permanence, informs his internality, even by the time of ROTS. When he bows to Palpatine, he can agree to the terms because he’s already spent the past three years haunted by what he’s done, already knowing well the shape of evil inside him. It’s what he’s been running away from, to reputation as a hero (a good man), and what he hopes is masterhood (vindication as a Jedi).
In the face of the Jedi’s persistent doubt and rejection, that protective self-image crumbles and he is left to confront the darker projections - the guilt, the secrets, like the wife he’s hiding, who he cares about most in this moment. Who has he been fooling? As a Jedi, he’s already failed.
So this all has more to do with himself than it does the Jedi Order’s faults to him, or even the politics of the situation. Anakin is lacking in the tools to actualize as anything more than the monster he’s feared himself to be, who Yoda always warns him he’d become. He’s fulfilling his own internalized hatred, and that started with the Tuskens. imo
(sorry btw, i don’t mean to be a prequel apologist, i also am disappointed with these movies, i just end up here when i have to think about it)