Yeah you'd think Tony would have a "rebuild my company/fortune" subplot or something, right? Maybe that's something the devs plan to release later. I don't think they wrapped up Thor's Loki/cult story either, so maybe there's a upcoming wave of subplot missions.
And I think there's a lot of possible reasons we don't have more diverse environments. Too little budget, or time, or imagination, or technical limitations, or legal barriers, or skill, or who knows what. I'm not a programmer, I didn't work on this game, I'm just talking out of my ass.
But I figure the fact that every hero had to be able to access each map and reach it's objectives had a hand in it too. In a game who's main purpose is to go multi-player with a diverse available roster, everyone's gotta be able to do everything, and that's a limitation. In a solo game that wouldn't be as much of an issue, the mission would only be open to qualifying characters. This game could do that, and maybe it should, but the idea goes against the open roster format. Hell, a future update will let us use the same character on a team multiple times so maybe they're headed in this direction anyway, and we'll get more specialized missions in the future.
I'm just saying, the moment in the campaign when Tony flies into outer space was cool as hell, as good as a MCU film, and it's a damn shame we don't have more content like that in post-campaign missions.