Looks like you were faster than me because I was planning to write something similar today. I wholeheartedly agree with everything you said and I'll even add a few more things you forgot.
1) Not only will you lose 3 companions if you want to recruit Minthar, but you'll also lose a bunch of characters you'd normally meet in Baldurs Gate. That's a lost of tons of extra content, quests, rewards, conversations...
2) Due to the fact that your decision to destroy the druid grove is not important for act 2, you get no reward for it and you can immediately switch sides, Mithara is literally your only reward.
3) Minthara is only a shadow of a companion. No romance, no personal quests, minimal amount of conversations and comments.
4) It just doesn't pay to be evil. It's actually ironic, because immoral and profit- and power-oriented evil should actually receive greater rewards. You'll just lose too much and you'll only get Minthar, who probably wouldn't weigh your loss even if she was a full-fledged companion.
Just another game where it's simply not beneficial to play as evil. I miss games like Tyranny. Its authors are probably the only ones who really understood what playing as evil guys should look like.
