People have been saying the super hero movie bubble would burst for the better part of twenty years now. So far they've all been wrong. In fact, there's more Oscar buzz around some of these movies than there ever has been before, and they still keep breaking record after record.
I doubt the bubble is close to bursting yet. It'll eventually happen of course, but I don't think its right around the corner.
But who knows, maybe Infinity War will jump the shark.