I could like this idea, depending on implementation. For me, immersive commentary is most immersive when it makes sense in the context of narrative, gameplay, and the practicality constraints set by the worldbuilding. What I DON'T want is combat to be like the Avengers movies where everyone is making quip after quip while in the fight not only of their lives, but of the lives of almost all those they know. That would be too cheesy. On the other hand, I can see the party utilizing their shared tadpole connection to telepathically communicate their thoughts on the fight with each other. Perhaps after a crit, a party member can telepathically say, "Alright, now just need you to do the rest," or "Take 'em out." Can definitely see Astarion vocally complaining about a character's incompetence though. But I think he would whisper it 'cause he's a sneaky rogue.
The Astarion comment actually gave me an idea. The reactivity of the companions in combat can be based on their personalities. Shadowheart would probably prefer the tadpole connection, or to whisper if nearby. Astarion would just whisper regardless of location. Lae'zel would be too focused on slaughtering her enemies to talk. Gale would use the tadpole, thinking himself to be awfully clever. Wyll would bring in some of that Blade of Frontiers showboating.