Let's level set. Compared to what, Pathfinder sucks as far as characters? BG3? Solasta? DOS 2? Original BG games?
In terms of most cRPGs I've played, I think both Pathfinder games have hit par at least in terms of side characters.
The only cRPG with companions that I would rate lower then Kingmaker in that regard was Neverwinter Nights1. It being the game I also rate on playability, so how poorly structured the quests were (like having to treck back to throne room, to be told by a companion in your current party that she want to talk to you in local tavern) does impact my perception of the companions, and how passive conversations were.
I would rate them lower then companions in both D:OS1&2 and BG3. I found Kingmaker's companions to be predictable and uninteresting though it's not my main issue with them. I have an issue with amount of content they have. Most BG1&2 companions didn't have much to them either, and some were annoying but none outstayed their welcome. JJ could be an exception but being an annoying old gnome was very much a point. All longer stuff that was there was good.
Kingmakers companions, on the other hand, will drown player on longwinded exposition dumps about their very detailed, dry backstories. As a game in general it did a sin of throwing out a lot of information, which might have a revelance to someone with world knowledge, while doing no worldbuilding necessary to make such self-indulgence justified.
So far I am not dying to spend more time with BG3 companions, but every conversation I had with each of them felt meaningful. I might not like some of them, but I don't like them for who they are, not because they are poorly presented or written. It also helps that players gets asked interesting questions when conversing with companions, rather then being talked at for paragraphs at a time.
Really, though, my way of judging is very subjective and based on my responses, rather then objective analysis. For example I would say that BG3 is better "written" then D:OS2 because I don't dread entering a new town and having talk to characters, like I did in D:OS2. I was genuinely displeased when companions in Pathfinder wanted something, though were writing end and overall questionable quality of the game starts is hard for me to judge. Kingmaker could have the finest writing in the industry and I would probably still be mixed on it as a game.
