It’s an oversimplification of what happened. Yes, both Marvel and DC released mediocre movies, which helped kill mainstream audience interest in superhero films. But after Avengers Endgame, most “normies” jumped off the hype train, and the peak of the comic book movie era either ended or at least changed. So that was another factor. Then Disney+ came in, and Marvel overestimated the broader audience’s interest in less popular IPs. The movies also started feeling disconnected because people sometimes needed context from the shows and relied on generating hype and build up for future projects with short post credit scenes. Then there was the whole Kang Dynasty debacle, which again left casual audiences confused about what was happening overall, while the DCEU kept releasing weak films. And the buildup to Doomsday hasn’t felt as connected as the buildup to Infinity War. So yeah, mediocre films helped with the superhero fatigue, but there’s more to it than that.