Marvel’s quality has been in freefall since before Endgame came out, and most people lost interest after the payoff. Their shows are terrible, and the last movie was so bad that even critics are lambasting it.
DC’s cinematic universe has been a clusterfuck from the get-go, and although they still make epic animated films their live action movies are rarely worth watching.
Hollywood has been blaming super hero fatigue- claiming that the genre is overdone and will go the way of Westerns.
The fact that people are still interested in Invincible proves that the genre isn’t dead, it is just full of shitty films and shows that nobody wants to watch.
Marvel hasn’t been in freefall, it’s just been extremely inconsistent. It went from Wakanda Forever (good) to Quantumania (bad) to GOTG 3 (very good) to Secret Invasion (bad) to Loki Season 2 (good) to The Marvels (Middling? I haven’t seen it).
But I do agree on the main point - “superhero fatigue” is BS.