Marvel Studios are the undisputed kings of blockbuster cinema, streets ahead of the competition in almost every respect. However, no franchise can remain bulletproof forever and the MCU finds itself under increasing scrutiny, especially as Wonder Woman's box office success and the upcoming Justice League could potentially reinvent the DCEU into serious challengers for Marvel's dominance.
Despite the success, the MCU is by no means perfect. Like every other blockbuster franchise it has its fair share of problems, but seems immune to the critical and commercial dips that plague many other studios. This could be part of the reason why many of these issues have been obvious in Marvel's output since the very beginning, although such a strict adherence to formula has definitely worked wonders.
However, 'franchise fatigue' is a very real thing. War for the Planet of the Apes was released a month ago and still hasn't crossed $300m at the global box office, despite being one of the year's best movies. There will come a time when audiences begin to lose interest in the Marvel Cinematic Universe, and the first step in preventing that should be solving the problems that have been there since the start.