I'm not entirely sure why we had to kill everyone in the grove, but what's done is done. I'm in tight with the Absolutists now.
That is the main issue with the "evil path" on a narrative level. There is little reason to attack the grove, other than doing the obviously evil thing.
The most simple way to improve this situation on the gameplay level would be to make tadpole powers only available for those who join the cult. You lose out on quests and great items, but you gain a set of unique powers. It's a far better deal than just getting a bugged companion. It would also make sense from a narrative perspective to have the option to join the evil cult for the powers they can offer.
They could have made the evil path so much better with almost a minimal effort. They didn't even need to create any new quests, NPCs or items. It would have been enough the distribute the existing stuff more evenly. They decided however to place everything good on the default path, thus creating the simultaneous illusions of freedom and abundance.
The fact that they recently allowed the knock-out method for recruiting Minthara on the good playthrough shows that they have 0 intention to give us a proper alternative. She was the only semi worthwhile thing you got for doing evil stuff. I have little hope left at this point.