I too liked BG 1's down to earth approach to companions including 2 Zhentarims, a Drow cleric and ranger from Rashaman who talks to his pet hamster. BG 2 as well, with Jan Jansen.
Forgive me my sarcasm but the companions in the original BG games also had their problems. Whilst I don't think the companions in BG 3 are great, I don't think BG 1 is an example of a game with good, down to earth, non "comic relief" companions either. If I was to use an example of a game with "down to earth" companions, I would have gone with Dragon Age 1.
Funnily enough, most of the companions in BG1 were actual characters some of the devs used in their DnD sessions way before the game was even in plans. Minsk for example is character which was invented precisely for these sessions as a half joke, but for genuine roleplay.
I know the characters backstories. I know that the reason minsc had a pet hamster for example, was because the person who played him kept getting knocked out and rping the hamster gave him something to do while everyone else continued combat. That doesn't change the fact that I still have an immense dislike for him and the first thing I do on any BG replay is kill him on sight. Minsc is, for me, the worst part of the BG games. I am not much of a fan of the Zhents either, nor of Jan Jansen. Viconia is a decent companion, but that doesn't change the fact that she is still "themeparkesque."
BG 1 and 2 had a fair share of what I consider to be awful companions, but fortunately it did balance those out with others who were not so bad, simply because of the sheer volume of companions there were. I still would not cite it as an example of a game with grounded companions though, its companions are nowhere near as grounded as those in other RPGs.
