Let's just say, for the hell of it, what if they did make him a barbarian? What would they make Karlach? I'm already annoyed that we get two druid companions, both good-aligned, even, and be missing out on other classes.
Maybe Karlach could be made a Paladin? and Minthara a ranger?
Honestly, having 2 potential druids has caused me the very slightest of pain. Especially, considering, one had lore as an established druid before for like over two decade (ok, she was technically multiclass), and the other is new lore (with a special). I suspect most "annoyances" are nothing but empty steam considering the horribly limited party size.
I bet we could have just as easily, if not more, survived with 2 barbarians, especially considering both would be fun (enraged throw boo > flaming engine). We survived with 0 bards, 0 monks, and, in most cases, 0 paladins, cause we had to off the only one there was.