This is fascinating. I think you're really onto something here. Especially Sirius of the OotP era. In both canon and fandom he's often seen kind of going off by himself and brooding, which god knows is what I (also an introvert) do when I'm stuck in a house full of people and can't escape. I think Sirius is also a performer who likes the spotlight, but then he crashes from too much people stimulation and needs to be carted off by Remus or someone for some quiet uh, restorative time.

And yeah, Remus is just way more chill and good at interacting and taking pleasure from that interacting. Maybe what's portrayed as shyness is actually just trauma from being a social outcast because of his werewolf status. When he's in an environment where he knows he's relatively safe (like when he was teaching at HW) he's good with everyone, even Snape.