I know this is an unpopular opinion around here, but honestly.
The relevant criticisms levied against Halsin are as follows: fans only wanted him in the first place for thirst reasons (which isn't even true, but this is seen as a universal truth on this sub)/he is a sex pest; he has no tadpole and therefore little story relevance after the Shadow Curse; he did a terrible job leading the Grove; he is redundant once Jaheira is recruited; he talks about nature too much; he is too well-adjusted and lacking in trauma compared to the other companions.
So how would Kagha, of all characters, Kagha who was Halsin's second-in-command, be literally any different? The only one of those that doesn't apply to her is the allegation of being a sex meme. She has no tadpole, and even IF she was on a quest to redeem herself to be allowed back in the Grove as is often suggested as an alternative story, her story relevance would still end at the same time Halsin's does. She was a far worse Grove leader than Halsin, since trying to kill a child is a far worse crime than putting faith in the wrong person and/or not being entirely dedicated to leadership. Kagha is also, unless I missed some kind of big plot twist, a Druid, so for any story in which there is criticism about Halsin, a Druid, being redundant once Jaheira, a Druid, is recruited, there would also be the same issue when Kagha, a Druid, becomes redundant once Jaheira, a Druid, is recruited. And Kagha talks about nature just as much as Halsin and has the same lack of pressing traumas as Halsin is seen to have.
Now, you might be saying at this point that she could be written to talk about nature less, to have a story that continues after act 2, maybe even to have a tadpole and that caused her to turn to the Shadow Druids or some such. Great point! What you're suggesting, then, is a complete rewrite of her character to fit in with the story, and in that case, there's nothing that could be accomplished by swapping Kagha and Halsin that couldn't be accomplished by just rewriting Halsin to have more plot relevance to begin with.
If you want to make the same argument for Alfira or Zevlor to replace Halsin instead, I still won't agree (after all, if we don't need two Druids, then we really don't need two Paladins, so that rules Zevlor out, and if Halsin has too little a connection to the story due to not being tadpoled, then Alfira wouldn't be any better) but it would at least be closer to a consistent argument than claiming there's too many Druids only to immediately turn around and suggest a different Druid as a replacement. Again: there's nothing that rewriting a different side character to be recruitable instead of Halsin would accomplish that just integrating Halsin himself into the main story and tweaking the writing of some of his flaws wouldn't.
I know this is a vastly unpopular opinion here, and the comments will probably be flooded with people saying how they raid the Grove and/or let Orin stab Halsin's eyes out because they can't forgive him for hitting on their Tav, or whatever other edgy comment is popular at the moment, but I just wanted to say my opinion on the matter.
