In the MCU, Loki came first, and the Marvel heads were hinting early on when Spider-Man followed that none of the events of the other movies would have happened without the events of Loki first, and / or maybe that Spider-Man just gave the final push after Loki - but none of the characters in either movies are aware of who broke it first (except Loki). But then, that was when they were making plans for Kang, and throwing in Ant-Man that was also intended to suggest that the quantum verse was common to all universes, quantum travel was going to play a part in the incursions (pushing the theory that they all played a little part in breaking the walls), but then they gave up on that, and that’s why the loss of some context made it weird.

We don’t know yet how Doomsday and Secret Wars intend to fix that mess, retcon it entirely, or just… handwave it away - but they’ll probably pull a random explanation. So far, it’s looking like Doom is angry at Steve for breaking the timelines just to have a child, so maybe he’ll blame the careless time travel that the Ancient One warned Banner about. Plus Doom seems to have a goal of his own about a potential dead wife and child, so maybe he’ll hold some sort of added responsibility.