well...I mean....it did find the formula. for a time the marvel juggernaut could not be stopped, it literally took over hollywood for an entire decade.The difference is that in the 70s even the blockbusters had a lot of variety. Jaws and Star Wars are very different movies. The MCU thought it had found the magic formula for printing money and made the same movie over and over again.
Its just that nothing lasts forever, and they stretched their model too thin without new innovation (and lets be honest some god aweful movies towards the end). And of course, there was likely always going to be some point when audience preference changed and superhero movies (no matter how good) weren't going to have the draws that they once did.