I'm going to preface this by saying I hate this champion and that he should be absolutely gutted.
Now, with my emotions out of the way, let me be serious and present statistics. According to U.GG, Heimerdinger has above a 50% winrate in 4 different lanes.
51.43% in Top.
52.57% in Mid.
52.59% in Bot.
52.23% in Support.
These winrates are all Platinum+. I don't know exactly what's contributing to his stellar performance across 4 roles, but from my personal experience, his turrets do entirely too much for him. In every lane, he simply afk pushes with the safety of 3 turrets around him (and movement speed around these turrets). Ganking him is almost as bad as ganking Illaoi, but he has kill pressure before level 6 and even after 6, it's still something to be wary of.
I'm not going to rant about what changes I think he needs because I honestly don't know. I just know that dealing with him is needlessly frustrating and killing his turrets seems unreasonably hard, especially by the time you can do it, he sets another one up for 20 mana.