It's not about a bubble bursting. Usually one or two come away as clear winners each year and the rest either do middling business or fail completely. Cramming more and more into each year is only hurting your odds of each movie being the one to really and truly catch on
It's like the CG animated films - they used to all do well, then studios started cramming more into each year, and we started to see ones that either came and went or flat out failed
You want to put each of your 150+M investments in the best position to succeed, and the way to do that is certainly not by flooding the market with them
My comment was more on the macro-level whereas you are referring to the fate of the individual films. The superhero genre has its hits and misses, but on the whole the genre is wildly successful and doesn't look to be fading away anytime soon.