totally agree. I made this comparison some weeks ago (McCain is closer to Murray and Maxey, than Seth and Forbes, as some mocks compared him). about his physical and atheltic profil we at least can point out, that he is pretty strong for a guy his size, especially his legs, and he doesn't hesitate to trow his body into the battle. (that's the main reason, why he is a very good rebounder, despite not playing above the rim).
we know, his measurements won't blow anybody away, but he should measure better than Sheppard. (my guess is, Sheppard will measure 6'1'' w/o shoes and McCain like 6'2.5", with a significantly longer wingspan).
and there is one aspect about athletic abilities, that isn't discussused as it should: "deceleration". McCain might not be the most explosive guy, but he can hit the brakes like few other players. (likely thank's to his strong legs). that's one reason, why he shoots that well in transition. if you can't blow by your defender, just let him fly by. it's his cobra maneuver. so yes, I would pick him over Sheppard.