Comparing Lee Sin's Ult and Tristana's Ult
Tristana's: Buster Shot Cost: 100 Mana Damage: 300/400/500 +100% AP Knockback Distance: 600/800/1000 Cooldown: 100/85/70 Range: 543 + 7 * Level
Lee Sin's: Dragon's rage Cost: Nothing Damage: 200/400/600 +200% Bonus AD Knockback Distance: 1200 at all levels Cooldown: 90/75/50 Range: 375
So the only advantage's Tristana's has is damage at early levels and range. Tristana is a marksmen but her ult scales with the wrong thing. Also Lee has a super great scaling of 200% bonus AD so at early levels it'll probably be dealing more damage than Trist's ult anyway. Lee's has a lower cooldown and no cost on top of all that. But this is all totally balanced because it brings "diversity" to League of Legends.
We still want him to be a burst mage though, so figure it out.