When the first iron man movie was announced, the character was a solid b-lister
The guardians of the galaxy were even more obscure during a comparable timeframe and had a different roster.
So b-listers can be elevated by good movies and at the same time a-listers in the comics can bomb (Thor 2, Thor 4, non-mcu: Spiderman 3)
How well-known a character is in my opinion not the deciding factor for the success of a movie. I’d say the quality of a movie and the ability to build hype (which gets harder with what appears to be superhero fatigue) play a bigger role