I had a home built vertical stick burner... it was sort of offset, but not really. Well, it was also a hybrid Gas/wood. I had one chamber that wood went in, with it's own air inlet, that could be adjusted to allow more or less air in... the gas burner was under a 3/16" thick steel plate, the wood sat directly above that burner... the plate would get hot and insure the wood never would be in danger of staying lit ( no mater how much you choked off the air). This heat went up the back of the vertical chamber, but the cooking grates were never directly above that area, so the heat and smoke went upward... and circulated around a bit inside too... exhaust was at the top in the front....
So, my experience with vertical is... the top is usually warmer than the bottom... but with something like the Copper Head, where the heat is clearly coming directly from the bottom and around the sides, this may be why in Bentley's testing it didn't seem to have this typical hotter on top bias...
The main advantage of a vertical, is it's easy to slide rack in and out and if it is a little hotter on top ( or even on the bottom ), it's very easy to shuffle the food around , just pull a rack out , reposition it, etc...
Usually on typical pellet grills they run hotter toward the smoke stack side... some apparently are very even across side to side, but on most I've owned, they have a slightly higher heat on one end... Not as easy to move cooking racks around, unless you have a rack system that came with the grill, or was a aftermarket system.