I've seen a few fan fics/art/etc. expressing that sort of sentiment re: Star and Marco, though obviously not in those exact words.
Like, "you're a princess, you're going to be ruing a kingdom one day, I'm just ordinary Marco Diaz, why would you ever be interested in me that way" and so on. I think Marco has enough shit in his life that he doesn't need an inferiority complex toward Star on top of all of it.
Went overboard with the shithole kingdom stuff just to express how Star/Mewni both have enough failings that Marco seems rational enough not to overlook. In the sense that she's only human(oid) too and he isn't putting her on a pedestal.
I guess what I'm saying is that the main appeal of the Star-Marco friendship to me is how they seem like equals and balance each other out through their weaknesses and strengths (even the Disney website refers to Marco as "the yin to her yang"), and so I never got the forced "class difference" thing some fanartists/writers liked to use to make their relationship seem less even on Marco's end. Basically I can take Marco constantly sperging out about romance with Jackie, but not over Star.