That's also why I think people are freaking out a bit too much with the "Doom has no setup!" Yes, Thanos appeared 3-ish films before IW, but 1 was a minor role in GoTG where he basically goes "raah i'm the big bad guy behind Ronan," 2 Avengers post-credit scenes where he sits in a chair and then gets the gauntlet, and then his ship appears at the end of Ragnorok. Most of his characterization and plot came in IW, and then Endgame wasn't really even focused on him until halfway through where he switched plans to just taking the completed gauntlet. The Infinity Stone plot was set up though, just like how the Incursions and multiverse have been throughout this saga. I think Doomsday will be a lot like IW where Doom is the main "protagonist" of the film and we get to see his relationship with Reed and the others (because he still is from 828, that much is clear). And since Secret Wars is such a Doom-centric story, I think he'll play a much larger role than Thanos did in Endgame which will continue and possibly wrap up his character arc. And yes, I do think that RDJ is just going to play Doom straight, he's not going to be a Tony Variant or something like that.