It seems that new GP's Q does not apply his passive

On-Attack =/= On-Hit

{quoted}

Well, his passive is an on-hit effect, his Q applies on-hit effects. Where is the clarity?

His passive is an on hit effect that SPECIFICALLY states it does not proc on Q.

Also, it does 10 + (10 per level) + (.4 AD). That's pretty strong, as at level 6 with 100 AD it is 110 true damage (refreshing every 15 seconds and any time an E barrel explodes). Getting that at a time when most champions have ~700-900 health is incredibly strong for a point and click ranged ability that you can refresh regularly (at 3 barrels, he can use it ~5 times with Q before he is out of barrels and cooldowns. That's 550 true damage on a point and click ranged ability, which at that level is over half someone's health bar in true damage alone).