I've said it before, I'll say it again:
How do you follow up 11+ years of world/character building, with 22 (?) movies, that culminated in one of the largest story lines in Marvel Comics history? The Infinty Saga is a tough act to follow, in fact almost impossible to follow. Add in the actors/characters that made that amazing magical ride so awesome leaving their roles = a recipe for "failure", or at the very least a massive let down (which is exactly what we're seeing). They were never going to be able to keep up the same pace and/or quality going forward. Anyone expecting that (and I can say I was a part of that hopeful group), was being unrealistic in their expectations.
Is the genre dead No. But it's certainly lost its lustre. Can they bring it back? IMO, not with the actors they currently have, nor the story lines they're currently pushing. Though, I do hope I'm dead wrong about that. Time will tell.