Looking at Serebii's pages for each of them.
They each have equal max attack, and Dragonite has higher special attack. T-Tar has the higher max defense, but Dragonite gets a higher speed.
Dragonite can learn Fire Punch, Thunder Punch, Thunder Wave, Aqua Tail, Dragon Dance, Ice Beam, Thunderbolt, Earthquake, Brick Break and Flamethrower (both 2x against ice), Stone Edge, Surf...
So...I'm still not seeing how Tyranitar is so overpowered and Dragonite isn't.