Letting aside her character, speaking of singing, Mikumo always stands out by a wide margin for me. They did a pretty good job choosing her VA. Kaname comes as a far second. But I can see why she is not leader material (no one but Mikumo tbh). But she has this cozy vibe sort of (kinda like Hisomu from Kiznavier) that for its nature doesn't fit well with being the front leader of a music group. This vibe was straightened by her initial call to Messer that also felt quite concerned.
So basically Chuck and Mirage can be affected by the Var syndrome. mmm, they are the last wagon wheels. So they can't improve much from the point they are in term of skills. And the only option for Mirage to get better is by sync with Hayate. Considering that they couldn't take down Messer, three vs. one, I'd be a bit concerned as their captain too. But at least Hayate can be boosted when needed, if we ever will get some serious fight.
Well, if anything at least all Mirage outfits are awesome
But seriously, I don't want to see her going into Var mode!!