i play heimer adc when my support locks something stupid, or if the enemy team locks a really insane bot lane that just shits on most other things like Cait + any sup wit CC for example. Also I lock it first pick sometimes when I don't want to get counter picked since he is so self sufficient.
First thing is to destroy the turrets without taking too much poke, this isn't actually too hard and his timers to place down turrets is actually kinda long, so the longer the lane goes the better your chance to kill him early.
Also don't walk in straight lines, like ppl telegraph where they are walking or going so frequently that it makes hitting those E's and W's pretty simple against most, you have to walk in different directions, not just in straight lines. That's probably the most important thing
Honestly when I play against Heimers i don't feel like he is too strong, maybe cause i play as him i know how to play against him?
Anyways i usually play Sivir or Xayah against Heimer, with sivir its just basically to play a super safe lane, i'm not looking to kill him really unless he eats Q's and more than likely he can't kill me since i can just E his E..Then I can W and knock down most of the turrets.
The other part is punishing him when his turrets are on CD, it's actually pretty easy to tell when the Turrets are on CD. If you noticed he isn't laying any down then chances are lol he doesn't have any charges, if you have a all-in champ / support setup then that is the best time to really pressure him.
I think most ADCs can do fine against, I remember a Aphelios who i had a lot of trouble with as well since he can do a lot of things that Heimer can do.
I really think it's just about picking your spots and recognizing when but also just learning how to path better. Most ppl in low elo only walk 1 direction, many don't use any sort of Attack move or anything..So if you just walk straight and just assume you aren't gonna get stunned up then that's your first mistake right there. Learn how to walk up then back then path in right to left sorta stuff with the goal being the same destination but you take a lot of different directions to get there.
If you are Janna I think she is a fine support into heimer, you could just shield yourself and take out his turrets whenever you want, then just W and Q.
The thing you don't want to do is go full on heavy commit cause that's actually how heimer gets ahead, when ppl get impatient and just want to brute force into all of his turrets when he still has Flash and R up and basically everything, it's like one of those things where it's not a good move, more than likely at least 1 or 2 of u will die if I lay down a RQ and hit a E on 1 person, now I'm fed and you are behind and that's where you mess up, you have to be methodical with how you handle it but at the same time not insanely passive or predictable..I want to stress that playing super passive is not a good strat either, you want to challenge him without eating too much poke and that's generally not too hard early; his all in becomes stronger the more predictable you play but also the more passive you play, since passive play generally means you are going to be eating a ton of poke from him.
OFC if that's too much you could just play Garen Yuumi and chill for like 5 levels and then @lv6 you just all in and kill him easy..