The brown bear is probably a bit too strong for the early game of BG3. I bet it would tear up a lot of weaker enemies, like the goblins. In DnD, your DM can prepare encounters for your party and adapt on the fly. A video game could be made to, but I don't expect them to do that. I would be okay if it unlocked at level 4.
That said, polar bear sucks big time. I used it once, and that was only for the hit points. I ended up losing that fight anyway.
