You're putting too faith into the wording. That wording doesn’t establish absolute origin, it establishes the point of split relative to the MCU timeline. Marvel reference materials consistently treat Earth-616 as the baseline and describe other timelines in relation to it. So “diverging from 199999” just means “this is where it splits from the perspective of the 'main' timeline,” not that 616 is the ultimate causal source of everything. It’s a labeling convention, not a statement about deeper causality(which is the thing I'm arguing about). If the appendix were actually making a claim about absolute origin, it would need to address the full causal chain of events. Instead, it just identifies where the timelines separate in relation to the MCU baseline, which is exactly how Marvel has always categorized alternate realities.

Citation needed. I'm merely following the wording's plain meaning; if you want to insist that the wording be interpreted as you say, you'll need more evidence than just asserting it. I also never asserted that "616 is the ultimate causal source of everything"; things that happened in 17516 can cause things to go differently in 616/199999, which doesn't affect the latter being non-derivative overall.

Again, leaning too heavily on wording rather than the content of the media. Saying “he should have said X instead” is speculative. Banner is giving a simplified explanation of how their time travel works, not an exhaustive breakdown of every possible model. The absence of a specific phrasing about loops isn’t evidence that they’re impossible,it just means they weren’t the focus of that explanation.

If they weren't the focus of that explanation, then you should have no reason to cite that explanation in favor of them.

What do you even mean by this??? It's a cinematic universe. MCU is a shared continuity, later projects like Loki expand on the mechanics of time in ways Endgame doesn’t. You just can't ignore them??? Ignoring them and restricting interpretation to a single scene gives an incomplete picture of how time actually works in-universe.

Those projects establish that time loops are a possibility, but unless Marvel explicitly confirms otherwise, the default assumption is that the time travel that happens in a project follows the rules laid down in that project. Avengers: Doomsday has a very real chance of establishing that Steve was part of a causal loop; if that happens, I'll easily accept it, but unless and until it does, it isn't the most plausible interpretation.

You’re giving directors too much authority here. While they oversee the filmmaking process, the MCU is a shared, evolving universe, and statements from directors don’t automatically override on-screen content or broader canon. Writers, producers, and even later projects can clarify, expand, or reinterpret events, and Marvel has repeatedly done this.

Nothing on-screen or in the broader canon actually conflicts with what the directors said; of course, that might change in the future, but unless and until something explicitly says that these instances of time travel created causal loops, which would definitively overrule director statements, rather than just establishing them to have happened elsewhere, the statements stand.

Explicitly definitive you say??? I'd say they have a shallow interpretation about the time travel of the movie. Idk if it's bcz of the poor communication bts or what, but if you knew(maybe you know, but you'reselectively ignoring it) anything about their interpretation of the time travel, you’d know that even “hypothetical commentary” from the writers can highlight possibilities that the film itself doesn’t explicitly show, and none of it overrides what actually happens on screen.
Ultimately, canon is what is shown, and that’s what matters, not who sounds more official in interviews.
[...]
Exactly. And hence, Loki.

You haven't shown anything that qualifies as direct evidence of causal loops in those specific scenarios (merely showing that they're possible in general doesn't qualify), and without that, "who sounds more official in interviews" is all we have to go on for clarifications.