Minthara is mind controlled at the start of the game, Halsin holding it against her after you rescue her and release her from actual mind control doesn't hold up either. The exclusivity is just to be gamey and as a cheap gimmick reward to show choices matter while weighting the game against certain choices so they dont have to matter

anyway why I logged on
https://www.tumblr.com/alicelufenia/760330287990407168?source=share
this post just came up on tumblr of a way to get Minthara's full plotline without losing Wyll & Karlach and worth the read

Minthara is the best character and she NEEDS to be recruitable if you side with the grove!
Also- I support the important thread in the suggestions: Let everyone in the Party Speak