But as far as companions are concerned, I'd be okay with BG3 having companions like Harrim (pf Kingmaker), for example. Not necessarily evil, but just neutral weirdos with their own fun spin on life and fun interactions. I feel like game suffers from every NPC being romance-able, and we're missing out on funner companions as a result - I'd like to have a kobold buddy, or a golem, or something! The world of BG3 is so whacky, but companions are all so grounded

Totally agree. It's very unfortunate that they chose to make all companions romanceable and by consequence limiting most of them to young, medium size humanoids.
It's not even that they're all romanceable that's the problem. It's that they're all sexable.
It is completely possible to have a non-sexual relationship. Since relationships are not defined by sex. So you could have a romance with say a golem, just one where you don't end up banging or having 40234537434 patches to improve kissing scenes.
I mean there's Wyll, I don't think you can sleep with him, you can romance him sure.
ay as them which means they have to fit into the narrative of "Gets tadpoled > Finds a party of other tadpoled people > Said people try to get in bed with you > Become squid". So having any more unconventional characters simply doesn't work, like having an Origin character Golem or Skeleton literally cannot function with the base plot point of being tadpoled.
There's of course characters like Halsin, Minthara, Jahera and Minsc which are non-Origin companions where such unconventional characters can work... But these were last minute companions and implemented purely for fanservice anyway...
Actually Jahera, Minsc and Minthara weren't last minute companions, they were literally Datamined during the EA days, Halsin however was the only one that wasn't Datamined as a companion, instead of Halsin we would've gotten Helia the Halfling Bard was who was planned and then cut for some reason, Helia was also planned to be an Origin character.