I think it's about 50/50 at this point as to whether AoS still belongs to the "main" MCU timeline or whether it spun off into its own timeline at some point/was always its own timeline. There are arguments in favor of both points, and the only official word falls short of even drawing a distinction between the two. So any attempt to make sense of the the situation is headcanon and fair game for speculation, so there are no incorrect ideas here, IMO. Also, IMO, the combination of behind the scenes production conflicts and a complete lack of consistency regarding the nature of Infinity War/Endgame's time travel is a blemish on what was once one of, if not
the best example of a consistent film/TV universe out there. I would have loved to see the fallout of Infinity War across the entire slate of existing Marvel TV shows, but even failing that, this entire issue could have literally been resolved with 1-2 lines and yet they chose not to. (I'm not looking forward to a similar situation with Sony's standalone films potentially tying back to the MCU for this reason, but we'll see what happens.)
If AoS was "always" in its own timeline, (that is, during its entire run as opposed to branching off from the MCU as a result of one of their own time travel events, which is also still possible), then here's another retcon theory: Captain America did indeed spin off his own timeline to be with Peggy in Endgame (a still-debated topic, but let's assume for this theory that he did), and that
this is the timeline AoS takes place in. This would maintain the connection to the original MCU and allow events to play out more or less the same way they did in the films through Infinity War. Perhaps Old Man Steve stepped in with information to stop AoS timeline's Thanos from beating the AoS timeline's Avengers, which explains why Thanos was mentioned once in AoS but the Snap was never addressed. It would also explain why, if AoS is a separate timeline where Thanos was (apparently) defeated, Dr. Strange didn't see it in Infinity War: it wouldn't exist unless they succeeded in defeating Thanos in their own timeline, causing Steve to go back in time and create the AoS timeline. After this, Old Man Steve would return to his original timeline to pass on his shield as seen in Endgame, since his counterpart in the AoS timeline was still around and thus it wouldn't need to be passed down there.
Phew. (This would also be a comfortable place for the rest of the pre-Studios TV shows to live, if needed.) It also makes Steve indirectly responsible for Coulson's resurrection and post-Avengers SHIELD career and family, which I think he would get a kick out of.
On the flip side, I think it is possible that in the aftermath of the Snap, there would be a lot of denial and some premature attempts to continue living life as normal,
especially if some areas happened to be harder hit than others. There's more wiggle room for some of the events of AoS and Runaways to take place post-Snap than I would have thought six months ago. Maybe closer to 50% of everyone vanished from San Francisco and New York, but LA happened to have fewer people per capita snapped or somesuch. Judging from recent experience, this could have led people to be
less sympathetic towards victims of the Snap,
less affected by it, and
less likely to mention it. In some ways that's an even grimmer scenario than the one implied in Endgame, but it's unfortunately not as unrealistic as I used to think.
