The only time I managed to "solo power level" in a divinity game was in Divinity 2 Ego Draconis. I went to the orobas fjords (IIRC) very early and just "sniped" out those easy 3K-4K experience per kill.
I don't kill NPCs. Most games I encountered that don't encourage NPCs being killed attached little experience reward for killing the NPC. Added with the negative reputation mechanic, it makes killing the NPC all the worse. Now as the OP stated, if the player's issue is killing NPCs out of frustration, then that's a different matter.
There are many different types of players, the ones who like puzzle solving, those who aim for the best killing machine (power playing), those who just hack and slash, and these are just a few.
I don't know if I recall this correctly but I think I remember reading from a manual of a Divinity game of the developer being proud that their game enabled the player to play the way he/she wanted to. I think that's the entire point why they made these things possible.
