While I don't necessarily disagree with you, I do feel it's worth pointing out that WotC's idea of a multiverse is different to Marvel's.
The MCU's multiverse is more parallel dimensions, where you have multiple versions of Earth and multiple versions of Loki and whatnot.
While WotC has snuck some of that in with the First World and its echoes, with multiple versions of great wyrm dragons, their multiverse is mostly extraplanar and extra-planetary. Toril's not the best example because it has its parallel sister world of Abeir, but when WotC talks about the multiverse, they're not talking about multiple versions of Krynn, some where Takhisis won and some where she didn't, that sort of thing. There aren't any stories about Toril-616 Elminster having to fight his evil twin from Toril-12345, either.
So yeah - I mean, I'm someone who prefers to keep my fantasy worlds separate - I don't really want someone from Krynn traveling to Toril, or someone from Athas showing up on Eberron - but it's still a different kind of multiverse than the one the MCU has.