Looking back at the MCU fascinates me as a comic meta nerd.
Most of the Avengers outside its founders and especially the Big Three (of Cap, Iron Man, Thor, Hulk as the fourth now that he's regained core member status) really aren't meant to be solo characters and so their sequel attempts are obviously falling flat. Even Ant-Man was a founding member yet he became equivalent to Martian Manhunter as a founder who remained in the team book and thus never really got many solo adventures, and Wasp is like if Robin became a founding Justice Leaguer. And even the Big Four, while solo book leads with their own distinct corners of the universe, are decidedly B-list in sales and pop culture till the MCU compared to THE A-list solo lead, Spidey. And per how Marvel Comics's big selling point was interactions between characters of course the guys with solo trilogies truly shone as, well, the Avengers. Assembled. This is in comparison to DC, whose A-list are solo book heroes and function best as such, and as beloved as the teams of the JL and Titans are... they really aren't ensembles from the ground-up like the Fantastic Four, X-Men, and the like are.
Nonetheless I was excited very early on to see the Big Four's solo trilogies be... well, solo trilogies. I think it would've been really cool to see the Big Four flesh out and distill their solo corners to the public in the EXACT same vein Batman and Superman the Animated Series did for those guys, and Marvel Comics could've seized the chance to have both strong A-list solo book heroes (outside Spidey) AND teams (no one's denying the X-Men and FF blow any pure-ensemble DC teams out of the water) alike for an extremely strong core universe. But instead Cap's third film became Avengers 2.5 (even if I quite liked it) and Thor became a duo Thor-Hulk movie, when perhaps they could've had a second solo Hulk movie somehow to flesh out his hunted wanderer status, then a threequel post-Ultron as Planet Hulk leading into Love and Thunder. And yeah yeah I know Hulk's movie rights... but still. And so they followed the game plan that actually happened and by the time we get more solo Cap stuff it's Falcap and no one cares anymore. At least Iron Man got his own true trilogy even if they wasted the Mandarin (and I liked the twist, but still) and his other "big" enemies and/or storylines.
And again, the Big Four have the most meat on their solo bones and they still ended up struggling a bit for material, film rights or not, right? How the hell could they do solo Captain Marvel films with how little material she has outside external factors like Brie Larson's unlikability? Shang-Chi? Heck, even Black Panther? If they played their cards right that shouldn't be an issue of course, but they didn't, and now it's a muddled mess on who's who and big name and what's what for threats and all that. And part of that is because those guys really never were meant to be solo heroes, but ensemble heroes as part of the Avengers, the level that say the JLI or Satellite Era Justice League members were.
We all know the MCU got real lucky with such a long winning streak, but that's all the more so considering they almost but didn't quite manage to turn the Big Four Avengers into solo leads on the level of Spidey and the JL founders. But ultimately they didn't indeed, and once the MCU truly dies down these guys will likely go back to their B-list status in even comics culture even if they'll always be rightly core/A-list in Marvel's universe and meta itself