Yeah, the problem is: you get so much good loot and items from killing Minthara, Dror Ragzlin, Gut, etc.
If you kill the Grove, the loot distribution isn't comparable at all. There should be some kind of quest reward from Minthara - item(s) you could only get if you went evil and that synergize with the Absolute's branding.
Think about it: why did Larian create an option for you to get branded, use Absolute items that can only be obtained by killing the people you're "siding" with, and still be evil
I've believed so far that they're limited since, aside from being quite OP, being branded with the enemy's seal might lead to rather terrible outcome. Like the amount of tadpole use, who knows what the consequence is? "Good" characters are unlikely to want the brand, "bad" ones don't get the loot. Only a niche population has posession of their character in the future
