Eh, I've seen it cut both ways (as someone who GMs 90% of the time).
Had a player I was friends with, and roommates for a while, who was a huge 'spotlight hog'. Since some players are quieter and less assertive, I try to make sure each player gets at least one 'spotlight moment' each arc. And this player was real bad for always kinda muscling into other player's 'moments'.
After having multiple talks, eventually just had to kick him (cause he didn't stop), which has pretty awkward considering 'roommate'.
So I'd take players that need to be coaxed into RP over players that have main character syndrome any day (though, of course, ideally all the players just RP readily but politely).
I'd say the key difference between a 'spotlight hog/main character syndrome' and 'a player who RPs a lot in a group full of quiet people', is does the player also start talking/engaging whenever the spotlight is on the quiet player.
Because I think that's the real rub; that difference between a player 'dragging' the less engaged players behind them (good and fine), and a player who can't allow themselves to step back and let someone else be the main character for a single scene.
For sure. Like a lot of 'social stuff', context matters a lot.
Groups are different too; a table full of engaged RP-heavy characters can work, but put one of those players in a more quiet group, and suddenly, they can talk over everyone and be a 'problem player' (or vice versa; quiet player an a very social group).
I'm a very social player and even I can feel like I'm talked over sometimes in a very engage RP-heavy group, just because I've trained myself not to interrupt people.