If you want to see Captain Marvel go very wrong (even wronger than at DC), check out the earliest AC books. Bill Black created "Captain Paragon," a mysterious hero not seen since the mid-1950s who returns. It's not only clear that it's supposed to be Marvel in the general sense, but there's also a pile of references to Eternity, wizards, and so forth, and there's a handful of spots where the letterer goofed, and he's referred to as Captain Marvel.
Basically, as I recall, he shows up, falls in with some hippies, drops acid, accidentally kills his ghoulish arch-enemy (who doesn't seem to be a reference to anything from Fawcett), and while flying off in grief, gets captured by aliens who use his power to create a superhero of their own. Yeesh!
Since then, to make the character less of a shoddy copy, he was (as far as I can tell) recast as an Old West crime-fighting cowboy who was captured by a secret society and transformed into an immortal superhero.
