[She doesn't really relish the comparison, and it's clear on her face she can't keep from getting cross, glowing a little more harshly - whether that happens when she's compared to Sollux or with the indirect affirmation that Feferi is more charismatic than her is hard to say.]

You could say that, but I'd say it's more nuanced than that. Interspecies communication requires both confidence, comfort with your mode of discourse, and charm, politeness and kindness; I think she's the only one of us who has both in sufficiently high measure.