The Marvel Cinematic Universe is built on lesser known characters and not just following what was established.
Not sure I really agree. The MCU didn't have access to the best known Marvel characters (Spider-Man, X-Men) but Hulk, Captain America, Iron Man, Thor, etc were still reasonable well know and popular and they formed the basis for the franchise. Furthermore, in the movies, while they didn't follow the storylines exactly, they largely lifted plots and other elements very directly from comics. I'd actually argue that the early MCU gave the audiences
exactly what they wanted from those characters - a boy scout old fashioned Captain America, an intelligent and philandering Tony Stark who improves himself, a Thor and Loki complicated relationship,
etc.
In contrast to (for example) Man of Steel that was a Superman was very few people wanted to see and was a disappointment that was exacerbated by a Dawn of Justice that virtually no one liked. Mainly because they did
not follow what people wanted to see for those characters.
Or to use more recent examples....
Top Gun: Maverick was basically a copy of the original film, rehashing all the same story beats and going out of its way to remind the audience of the previous film.
Barbie presented itself as a bubbly fish out of water film, but subverted expectations by being a more heavy handed commentary on patriarchy and being a woman in modern society.
Both films made well over a billion dollars.
Point being, there's no "right" way to use an IP. Sometimes catering to the masses' expectations works best; sometimes going against the grain is better. My comment to you is that making a blanket statement that doing what people "say they want" automatically being bad is just silly because than can be a good strategy if executed well and in the right circumstance.