It's saturation, Disney+, and the inflation/recession combo.

All it takes is a few misses and people will wait for streaming.

Me, I'll watch everything Marvel but I can wait, so when I was ready to go see a movie and it came down to Superman or Fantastic Four, the choice was easy. Superman delivered exactly what I wanted and needed.

I don't think this is superhero fatigue, or at least that's a lower issue on the list. It's Marvel (formula) fatigue especially, and I think they will right that ship soon.