Oh dear, Marvel success does not trouble me, anymore than Twilight, Fast and Furious and Disney live action troubles me. I know the film industry and know that these kind of movies have the most success. that should not trouble anyone who just knows films and Hollywood. If anything I feel it is the other way around.
I know this first hand because I saw , read and replied to many of the reaction when Avatar surpassed Endgame again at the box office, Some acted very negative and even were throwing bad shade at James Cameron and I was one of the few who just pointed the fair
truthfulfacts that both Endgame and Avatar both got re-released to get to the number 1 spot.
Also Avatar just has more film making advantage going for it that makes it technically very easy to get back to number 1 as we have already seen with another Cameron movie that was re-released with more film work done with it that it made go past 2 billion, that would be Titanic and I am not even a big Avatar fan but funny, I was never called a hater or just not liking Cameron films when I said Avatar was not as overall as good as other Cameron films even if it is the number box office movie again. I wish some will also use that logic with me here and comic films of Marvel, DC and whatever.
Also if you notice I don't really talk much about success in terms of money, I care more about the artistic aspect of movies. which is what I mostly talk about here. you can discuss much with box office or streaming but you can sure discuss what is good or bad VFX or which story you think is getting dumbed down and which isn't.
The OP is implying Marvel is stuck, he even thinks their Disney shows are not as good as their netflix shows even Iron Fist
and all their movies of recent are just alright on in his words sub-par . I think that is pretty fair from my own POV to say, what marvel needs is to grow from where they are to the next stage of what we know the genre can be.