Because Marc? Hardcore, badass man of adventure? Is boring.
But Steven? Goofy, bumbling museum nerd? Is funny.
Isaac is clearly having a great time playing Steven, investing the character with a roster of iffily-accented Cockney vocal tics and other bits of business to flesh him out and make him someone we can care about.
But in the underwritten role of Marc, Isaac seems determined to disavow his natural actorly charisma to play a glum, laconic cipher. If he’s going for “lone wolf, wounded by his past,” he’s ended up closer to “surly, jet-lagged office manager.”
The net effect is to reverse our rooting interest—instead of impatiently waiting for Steven to let Marc take over and unleash hell, we find ourselves hoping Steven can keep hanging around, so we don’t have to deal with Marc and his one-note, dull-as-dishwater machismo.
Moon Knight is mostly not about Moon Knight
You might notice I haven’t gotten around to Moon Knight himself, yet. You know: The titular role? The guy in the white suit who’s on all the promo materials? Looks like what would happen if you mummified Deadpool? That guy?
That’s because the show doesn’t really get around to him a lot, either. Oh, he shows up from time to time, as he’s the avatar of the ancient Egyptian god Khonshu (who also shows up a bunch, mostly to neg on Steven—he’s voiced by F. Murray Abraham). (If you’ve seen Inside Llewyn Davis, it’s fun to imagine the bird-skull-headed mummy god telling Steven/Marc “I don’t see money here,” in their every scene together.)
Both Marc and Steven can become Moon Knight, it turns out—and the show has some fun with their divergent takes on the hero—but Moon Knight is mostly the Steven and Marc show.