Ideas about Rumbles E

I love the new ammo system. It makes last hitting easier. But I got a idea how to improve Rumbles Late game. Made the E ammo recharge Cd lower per level. --> at rank 1 cd is 5 sec --> rank 2 4.8 sec cd --> 4.6 cd--> 4.4 cd --> and at rank 5 E cd is 4.2 sec. Not sure if this could be toi op but Rumble really falls of Late game. This is in my opinion the best way to balance him.