I suppose I do favor quantity over quality to a certain extent, but only because its usually presented as this stark either/or. I'd rather have both, surely, and I think you're right that the BG2 companions had a bit more going on. They each had a questline, and some major plot interjections, or an associated class stronghold area. Even Misc had the "which Witch?" thing, where he'd try to dime-in on Aerie or Viconia as his new Dhynaheir replacement depending on who was rolling along. Though I think you might be right there too, that he was like the only BG2 Companion who didn't really have a questline, and yet still ended up being the most iconic BG character somehow, which might say something about how much players really need to work with to make someone memorable.
The problem with good and interesting as I see it, is that it's still pretty easy to hard pass if a player just doesn't like their voice or has an "I hate their stupid face!" hang-up, or simply finds that a companion's char or class archetype overlaps too much with their own MC to be tolerable.
Part of the problem they have right now in BG3 is exactly this, that some people fall passionately in love with a particular companion Character while others totally hate that same companion, purely for reasons of taste or fit. Right now we have only 5 companions, and it seems they are meant to be the villains, even though none of them feel particularly villainous right now. One can maybe assume that we'll have more than 5 eventually, perhaps we'll get 8 or 10 altogether, but that still seems like not nearly enough.
I think Halsin has plenty going on to qualify, the guns alone are shoring up his character for some. If all they have to do is change a line or two of dialog about what kind of Druid he is (not quite arch) to make it work narratively, that seems like a simple fix.
