Not exactly surprising, thought it was already known that the "lower" MP levels are more efficent due to the immense health increase on the higher levels.
Though I'd like to see the numbers for a say, decently geared TR monk on MP2-5 or so, I'd assume that'll get more essences.
Probably all other classes can go as low as they want due to not having WotB and the faster they kill, the less likely they are to get stuck in some CC.
KingKongor is one of the elite Barbarians, he's been posting useful videos since the game's release and he's a member of this community for a while now (maybe not posting/discussing much, but still he's been here for a while) - it's not like those guys who create an account just to advertise).
Anyways, even if you are going to criticize someone posting videos, do so in a civil manner. Name calling is absolutely unnacceptable.