JT is already way better than Varejao. If you look at statistical trends, Varejao already exhausted all of his potential by his third year in the league (when he was 24/25 years old)--and because his game is predicated around generating energy both offensively and defensively and not really developing any sort of skillset, you already know what you're going to get. Another relatively interesting tidbit is that in terms of physical tools for a big man, he's pretty good in the league--but he doesn't rise up above the clouds with his abilities. For someone with pretty good mobility, he doesn't rack up too many steals. For someone who jumps pretty well and has a constant motor, he doesn't get too many blocks.
Instead, five years into the league, he's still a foul maniac, and when you're that age and still essentially the same player as you were in your rookie year, just scaled to minutes accordingly, you can pretty much say that player won't ever improve again. He never had much of an offensive game, nor had the ballhandling abilities and controlled game to really develop any post moves; only once in a blue moon can hit a jumper. Came into the league as a surprise considering where he was drafted and because he was an unknown entity, but time has exposed his sameness and he's become yesterday's news--hence the Cavs want to trade him.
Jason is active and will fight for balls, but already at age 22 he was better than Varejao has ever been; Varejao put up 6.7 ppg and 8.3 rpg in his best year, but Jason already is putting up 9.9 rpg and 6.6 rpg--#'s I will definitely prefer, because showing offensive potential is as key as showing rebounding potential. Jason at times doesn't know how to adjust to the speed of the game yet, but he's only a rookie, and he's already intriguing as a guy who can really rebound, hustle and score both inside and out intermittently. Varejao only did the two first things well, but the offense is the key here in separating a hustling role player to someone who can do much more. By getting minutes this year Jason's only learning more, and at age 22 with his hustle-rebound-offense combination as opposed to Varejao's at age 26 and only hustle-rebound combination, we surely know we've got the better player. And this is coming from a guy who was drawn into real athletic freaks like Anthony Randolph and JaVale McGee on draft day.