He's the worst companion mechanically. Berwyn sucks as well, but he at least prioritizes hp damage which is consistent in the early game. With Quin, if you didn't pick a Charmer he's useless, if you're not on manual control his AI is useless, if you didn't rush Cait quest to get her dancer form, or picked the pure hive ending for Bimbo Azzy, he's useless. And even then that's short lived, at least Brint, Arona, and Azzy are all interchangeable in their fighter/tank role, the minute you get Cait and Azzy, he goes right back to being useless.
Add Bubblelord's reputation and his propensity to right more jerkish characters (which sucks particularly in this game, because the writers rarely give you an opportunity to talk back to them) and you have a recipe for the least liked companion.
And even if all this hate isn't justified and we're just looking at it at face value, the key to writing a standoffiish character that's supposed to be liked is to give them a hook for readers to invest in looking and make them want to look at their side. Quin currently doesn't have that hook.