In terms of realism, of course, it would be much more interesting if the companions built relationships among themselves instead of hovering around Tav, and it doesn't require sexy cutscenes, dialog lines are enough, but it would make the relationships in the group much more like those of real people, and the game would feel less like a dating simulator for one.
There were hints of that during the Early Access days with Lae'zel and Shadowheart, but that got shafted completely safe for the few lines of dialogue they get after you make them make up, which is the extent of the additional banter between them. That they then proceed to be completely silent and non-interactive for the remainder of the game (that scene happens during Act 1!) shows just how little there is to the companions past their quest chain (which occurs in split-apart act-based bursts) and the romance.
I think that they should have stuck to their guns and kept the "whoever you leave behind in Act 1 stays behind" idea around instead of letting you have everyone and make them arbitrarily miss important story beats. Maybe if the player had to maintain a more tightly-knit party throughout it would have allowed for more interactions in those smaller groups. It would have made the game feel closer to the originals as well, where there was little reason to swap party members around on a regular basis and you instead picked a more or less permanent party that was pretty much set in stone after Spellhold. Instead they gave in and frontloaded all the game has to offer, giving little to no reason for additional runs if you can experience everything in about two at most, something that the lack of real reactivity and gender (basically, actually convincing romance) / race (the githyanki had one ending that only they could get with Lae'zel, but even that got taken away and given to everyone...) / class (there were hints of something cool if you played as a Shar cleric in EA, but it got cut in full game, for example)-exclusive content also plays into.
