Eh, I dunno about this angle. The infinity saga was also built on the back of C-level characters. Iron Man and Cap are global titans of the genre now, but that’s what the mcu made them — back in 2007 neither of them were much known or draws. Same for Thor, BW, BP. Hulk probably had the biggest pre-MCU draw of phase 1&2 characters and he only got one solo because of rights issues.
The fact that they were hobbled without access to marvel’s actual heavy hitters (mostly owned by Fox and Sony) and still cranked out 23 movies with that reception was insane.