I kinda disagree to be honest. Sure, there's been lots of entertaining movies of these characters on their own over the years, I guess the prime example being the Dark Knight trilogy. But things like the Justice League and these character's relationships with other superheroes (like Bruce and Clark's friendship) are fundamental to them in the comics.
The MCU introducing all sorts of insane multiverse shenanigans and just having infinite versions of every character didn't help things feeling overly convoluted, but I think to have truly great and faithful depictions of certain comic book characters, you need the teamups and dynamics they have when interacting with their broader universes.
Iron Man was a great movie on its own for sure, but RDJ and Tony's character really hit a peak when they started introducing Captain America, the Avengers, how he managed those crises and the Sokovia Accords, and of course completing his character arc from a selfish arms dealer to making the ultimate sacrifice in Endgame.
I'd love to see the DC characters get a chance at having such well-done arcs in their own universe, and James Gunn is a director that really knows how to deliver on those.