As a dedicatied Heimer player, I have to agree the OP. Heim's kit is just too broken and allows him to beat any enemy. Heck, sometimes I 1 v 5 in normals just for fun and WIN.
Seriously he's like three champions in one at least (1 Scientific Yordle + 2 Turrets = 3). When you add his grenade and three rockets that makes seven (1 Scientific Yordle + 2 Turrets + 1 Grenade + 3 Rockets = 7). Now this may be a bit of a stretch but seven is greater than five (7 > 5) so I feel like Heimerdinger's advantage on the Fields of Justice is too great and rather game-breaking.
Heimy needs a nerf since turrets, grenades, and rockets are op when all your enemies have are claws, swords, and daggers. Also seven is more than five.