@BCTheEntity keep in mind, the Warp Skulls are a relatively young chapter, and even their parent chapter aren't going to sacrifice their best senior marines to supervise the new guys. Yes the leadership of the chapter is relatively experienced, but they aren't quite the ancient, grizzled veterans you seem to be thinking of. "Tone it down" is kept vague to allow you creative freedom for this sort of thing, but the general idea is that yes, your character is powerful, because they've been picked to help lead a whole fucktonne of spess mahreens, but they haven't been around for fuck-off centuries like some chapters have, so being some kind of super-space marine doesn't quite make sense.
Also, on the note of feats. Feats are pretty well exactly why you get promoted, especially in the military. Someone runs up on a machine gun nest and rofl-stomps it while missing an arm and a leg to medevac their buddies? They get a medal, and some officer who's retarded(and they're all retarded, except the ones that used to be NCOs and even some of them get retarded if they drink the koolaid) goes "promote that man, it's good for pr" and now you've got an operator running the show until his take-no-shit-and-give-no-fucks attitude and tendency to send everyone home at noon gets him busted back down. You totally get promoted for being a badass, it just doesn't always stick because badassery doesn't always equate to good leadership, like you said. I don't remember where I was going with that, though...