If I want to watch superhero stuff, I rather go back to the classic animated series like Batman TAS and Superman TAS or the 1940's Fleischer Superman cartoons. Those shows were of high quality. Better than 99% of superhero movies.
I’m going to expand your original timeline window to make my point but one thing I will agree with is super hero movies have been poor as of late.
I make no secret that I’m a MCU fan and while not every movie was a hit, MCU phases 1-3 were good. In there, Winter Soldier and Civil War were masterpieces. Infinity War was epic, and while Endgame was a “small” movie within a spectacle. GoTG V1 was one of the best popcorn sci-fi movies in quite some time. Ragnorok was funnier than most comedies within a couple years. There were duds (Dark World), but for “comic book” movies, they were decent.
Before that, I know some people love the Burton Batmans (I hated them), but to me Nolan’s Batman wasn’t just good comic book movies but they were just good movies period.
Aquaman and Wonder Woman (1) were good, but the DCEU movies in general were trash. IMO, this contributed to the super hero fatigue. Pretty much all the post-phase 3 MCU movies have been mediocre to poor. Thor 4 sucked, and other than No Way Home and GoTG V3, I haven’t enjoyed recent films as much.
As for the original comment about animated stuff, Spider-Verse 1 was one of the best animated movies of any genre I’ve seen in a long time. Spider-Verse 2 is coming out this week, but reviews have been glowing for this as well.
Back to your original comments about post-2015 films, one thing I didn‘t see mentioned but I think impacted cinema and TV big time was covid. “How” movies were made, studio commitment/nervousness and money (not spending) all contributed to the drop in quality. I mean, i would have expected writing to had improved since everyone was locked up, but it was obvious especially for TV how covid affected quality.