I suspect the weight of the machine gun and the gunner at the very top of the vehicle does more to change the center of gravity than the armor. Also, the ctitic here is trying to sell against the humvee. He has his own vehicle he is saying is superior. He may be right but his perspective should be considered.
http://www.globalsecurity.org/military/systems/ground/m996.htm
You would think that these are even more top heavy.