So then yet another non-good companion?
I don't think the math really shows that imbalance. Remember, we are getting Karlach, Jaheria, and Minsc as well. And the latter two have been explicitly called out as exclusively good companions in the stream.
Evil Companions:
Asterion
Lae'zel
Minthara
Shadowheart(?)
Non-evil Companions:
Wyll
Gale
Minsc
Jaheria
Karlach
Shadowheart(?)
Even if you count shadowheart exclusively as an evil companion (and I'm more inclined to count her as good since she has such a heavily telegraphed redemption arc and siding with the goblins seems to lock you out of her as a romance option) then the balance is still very close, with a slight imbalance *away* from evil companions.
If Minthara is a companion for the evil path, then Halsin will also be a companion for the good path!

🐻🐻🐻
Unfortunately for the Halsin lovers out there, I don't think that is the case, since Jaheria is a druid, and we haven't gotten any indication we will have multiple companions of the same class yet.