I was about to post this to the bugs section. Since I received no XP from defeating the Commander.
I agree with Deemer. My friend and I tried to complete this challenge of defeating the Commander, it was certainly disappointing to not be rewarded after it.
Although I acknowledge Distant Stranger's point that we get enough to still level up, but... It's a Devil Commander who can essentially one hit kill/down most level one characters, and the fact that we were able to still defeat it was in my opinion quite a feat.

I would certainly love to see the appropriate amount of XP represented. OR at the very least, some XP, since we got none for the fight.