Mundo, Shyvana, and Amumu get to deal full damage with their AoE Abilities to creeps and jungle monsters. Why not bring him up to par with those 3 in the jungle?

Would that really make him overpowered?

Bump.

Why cant talon have his q bleed damage on a minion/NM ... it would make his jungle clear so much faster ...

I'm not sure they intended Hec to be a jungler. I think the reduced damage is to stop the lane from being pushed to hard if you're harassing the enemy with it.

make it so it deals full damage to neutral monsters but keep the 35% reduction on minions.

problem solved

Because he has much superior ganks than shyv/udyr/mundo.

Because buffs can have unexpected results.
It'll be better to slowly increase it if his jungle needs improvement, but giving it a huge buff can easily throw him over the edge.
And if you're going to compare jungle clear times, you have to compare all the other things junglers do too.

There are 2 sides of the coin:

Hecarim is solo top or jungle champion

Jungle he needs Q to clear faster, and i really would not make him overpowered.

Lane needs Q to harass

Everytime you harass youpush your lane
Do you really wanna do 200 damage to each minion to get some damage onto the enemy champion? Get the minions under his turret, where you can be easily ganked, is hard for you to farm?

Riot is trying to balance this. Putting it to an amount where jungle clearing is very good and wont push lane too much.

Amumu tears deals %HP, minions % is low, so not much pushing. Shyvana deals i a VERY small area, and it is damage over time, meaning you can simply juts walk away from minions dealing just a little bit of damage, instead of 200. And mundo burning agony can be deactivated at any time.