What is it about Mayo that makes you think he's so undersized? Is he closer to the shorter end of the height range for a 2? Yes, but not sure it's short enough to be making a point of. He'd be giving up a grand total of 2 inches in height to the best SG in the game, Kobe Bryant, and a total of zero inches to the second best SG in the game, Dwyane Wade. Eric Gordon, who will be an All-Star at the position very soon, is even shorter than Mayo at 6'3", and he's doing just fine on both ends in spite of his size, I'd say.
I'm not making a direct comparison between Mayo and the others' skill levels, obviously, but at the ground level, he at least has the athletic tools to do well at the position. He hasn't been able to get things together with those tools in Memphis. I'm guessing we'll be finding out relatively soon if a change of scenery sparks something, whether it's here or the other, more aggressive team that will eventually make a move for him.
BTW, this isn't a post in support of the Thompson + Greene proposal. His horrible inside touch aside, JT is still an important piece here because of his versatility as a 4/5. He's still young and unpolished enough to make his potential intriguing to the point where I'd rather not let him go yet.