Thrall would be extremely difficult to stat up. He has a unmodified stat of 14+ for each ability score, making him ridiculously powerful before his levels are taken into account. He's huge - Orgrim Doomhammer was described as huge, but Thrall was even bigger, so it seems he has a base Strength of 18. And he's completely ambidextrous, and quite intelligent, and wise enough to make a powerful shaman, and yeah he's a good leader as well. He's also tough, but I can't recall the exact description.
He was so well-trained as a gladiator he defeated the high level human warrior known only as "Sergeant" ... at age six. He also beat Warsong's three best warriors, while they were armed and armored and he was caught off-guard. I think even Drizzt couldn't match him in pure cheesiness (at a young age, that is).
He's practically a Mary Sue. If "Lord of the Clans" the novel were even slightly less awesomely written I'd probably be quite upset about the Thrall character, actually. He's next to impossible to replicate, and can only be done so at high level ... and there aren't any good rules for fighter/shaman/leaders so his stats would still end up weak. (Sort of like the 3.x Drizzt, Artemis Entreri and Elminster stats.) A Drizzt-clone is easy to stat up because you only really need to be a good-aligned drow and not worship Eilistraee. (Eilistraeens are their own cliche!)
Another reason Thrall-clones aren't found in DnD are stat differences. Orcs from Warcraft should have bonuses to Strength and Wisdom and maybe Con, along with penalties to Dex, Intelligence* and maybe Charisma. This is quite a bit different from the 3.x orc, which has penalties to Wisdom!
*Thrall has a naturally high Int score, before you apply the orc penalty.