For starters, I'm definitely one who considers canon to be just what's in the actual work, and whatever creators say outside of it negligible, to be taken into account if I like it and discarded if I don't (thanks for the very thorough training in that, JKR). Not that I don’t discard canon also when I feel like it, but if I say something is canon compliant, previous is what I mean. Hence, stuff that the creators say about Endgame is all in the discard pile when it comes to writing fic (I think, I haven't gone looking at the interviews, most I've gotten from headlines and fan discussion/reactions, and so far nothing they’ve said has been stuff I’ll want to include).
I have to say though, I find this whole thing a headscratcher, first because the directors and writers have such conflicting opinions of what happened with Steve at the end and how time travel in the movie works. They've obviously worked very tightly together for years, how can they be on such different pages? (Cue tinhatting about it being deliberate obfuscation so they can later decide either way.) Secondly comes the point of this post, which is the inconsistency it puts into Steve's characterization, if it indeed is a rigid time loop rather than a multiverse as the writers posit. The more I think about it, the more it feels like the writers had this clever (not actually that clever) idea, and when people question it (for good reason!) they double down on it even when it throws away the core part of their previously established characterization of Steve Rogers.
If we look at the three Cap movies, they all have the same writers, and a very consistent characterization of Steve. I recently came across a comment I made on a tumblr post pre-Infinity War, in which I said that even though the upcoming two Avengers movies looked like they were so crammed with stuff that there was a potential for it to be an unholy mess, one thing I wasn’t worried about was Steve’s characterization. (That one aged well :D) Back then, it was a reasonable expectation, which now leaves me confused because the insistence of a time loop means the Steve they’re talking about is a completely different one compared to the one we got to know in the Cap trilogy.
A lot of my favorite moments for Steve have been about his desire to act when he sees something that he considers wrong. He wants to sign up for the war because he doesn’t like bullies. He urges SHIELD agents to choose to do the right thing, not the safe thing, and shows an example. In Civil War he says to Tony, “If I see a situation pointed south, I can't ignore it.” He keeps pointing out he can do it all day.
And I’m supposed to believe he went back in time, knowing that Bucky suffered all those decades, knowing that Hydra was hiding in SHIELD, and did nothing? That’s not the Steve Rogers we got to know in the other movies. He wouldn’t stay silent just to preserve the timeline, he’d say it’s a pretty fucked up timeline and he’d try to fix things he could. Obviously there’s never a guarantee of things becoming better overall as a result, but it’s not a reason not to act.
If there was a time loop, and you inserted a Steve who knew about Hydra and Bucky in the past, you’d end up having a different present, because Steve would act. Or you’d have to ignore the very core of a character just to keep it from breaking into a paradox. Or you’d have to scrap the idea of a time loop and have a multiverse instead, one that accommodates for Steve taking action.
I know which route I’m going to take when writing fic.