I thought about it a lot and I do have to give credit to Larian for even creating an evil path, something that is really uncommon in crpgs. Most crpgs give you evil options but they are just variations of the same paths. Take a look at the underdark in bg2 - you have the option to be a real asshole but ultimately the story is the same. Larian tried to do something a little different.
However, I feel like the result is so bad I don't think it is worth it
I like the existence of the evil route too but agree that it's currently bad. But, it'd require a pretty simple change to vastly improve it! Just have Minthara explicitly promise you power from the Absolute if you give up the location of the druid grove and/or participate in the raid. You'd be able to join the cult with their recommendation. That's a perfectly valid (non-murder-happy) "evil" motivation: power at the expense of others. This could even work for more neutral or even good characters: you're trying to infiltrate this cult in order to learn more about the tadpole in your head and/or to eventually take down the cult: sorry tieflings&druids you're just collateral damage/it's for the Greater Good.
Larian wouldn't even need to significantly change the morning after scene with Minthara; it's perfectly reasonable that an evil cult would
betray people it earlier promised to help.
Just add a dialogue line or two referencing the deal made.
