Heimerdinger requires enemies and teammates alike to change their playstyle entirely
He's OP and I ban him every time.
He's not OP numbers-wise, but design wise as he requires everyone to change their playstyle in order to fit Heimerdinger.
Enemies are forced to play super passive in higher levels, and more aggressive players on both teams are made to suck it simply because 1 person out of 10 chose to pick Heimerdinger rather than another champ.
Teammates are also forced to play really passively in the higher levels because their enemies will be playing safe.
In lower levels, people just dive Heim's turrets and end up feeding him, and then all attention goes to Heim's lane while other lanes are ignored.
Either way it's not fun.