Whatever happened to Heimerdinger?

All he can do is splitpush and win his lane, not that I think he's weak or anything, but he can't roam very good and pushing can only do so much until it's lategame and you're down for 50 seconds because you 1v5 the enemy team. His ultimate turret can be destroyed quickly in teamfights and he doesn't have any reliable cc.

Two reasons:

1. He hasn't been touched for a long time and hasn't gotten any form of skins to increase people's attention to him
2. People are scared to use a champion so different than the norm in the current meta
3. Yasuo and Ekko counter him

Pretty much, nobody's playing him right now. It's not really that he's weak, he isn't, it's because there are better options. However, I do enjoy playing some Heimerdinger top lane and building Zz'Rot Portal and Banner of Command as a cheeky little split push build :^)

I see him all the time. He's his same annoying self that auto-wins laning phase and then becomes irrelevant by the end of the game.

You got lucky. He's not a common champ, but his mains spam him more than any other champ's mains.