Most champions have no mechanical counterplay against Twitch

But that's because he plays the macro game, and you have to beat him at his own game.

I've been watching a lot of high level top laners recently (not because I play top, mostly just coincidentally) and one thing they hammer over and over is that you need to be patient and wait until you see the jungler on the map. Yes, even if you really don't want to.

I'm not saying it's easy - even the Challenger+ players I watch make macro mistakes once in a while - but it's really stuck with me that if you make a play without knowing roughly where the enemy jungler is, and he comes and ganks and kills you, that's your fault.

Wards protect you from ganks, but, more importantly, they tell you where the one champion that isn't (mostly) stuck in a lane is. If the support or adc or mid laner is missing, even if your allies don't ping, you (ostensibly) know it because they haven't shown up on the minimap in a while. That's why towers are still so important even when they suck at fighting, even a tower with low how provides vision control and pushing power, and the enemy has to dedicate a champion to killing it.

The jungler, on the other hand, could be anywhere, at any time - until they try to gank, or path over a ward, and collapse the quantum entanglement of being about to gank your lane and about to gank another lane into one, clear state. Again, that's why wards are so important and deep wards are so powerful - having vision of a spawned camp, even if the jungler isn't there it tells you that he's off doing something else, and that it likely isn't farming.

Anyway, getting back to Twitch: he's indeed a special case, because he can slip past wards with stealth - but he can't fight or farm while stealthed. Every second he spends stealthed is a second he's falling a little behind on told and xp, and you can abuse that. If he's farming bot, and disappears off the map, pay attention to where the enemy jungler is - if he's running bot, back off! If he's running mid, back off! If he's top, both bot and mid should back off u til they see twitch - they can still get more farm and xp while playing cautiously then twitch can while stealthed.

If he's jungling, ward his camps, ward his jungle! He can't fight camps stealthed, and it has a long enough cooldown early that he's not gonna use it to sneak around his own jungle.

Pay attention to his jungle pathing, anticipate ganks, and understand that if you haven't seen him in a while, he's probably preparing a play - back off until you do see him.

Now all this is really really hard, and I suck at it all, so don't think I'm telling you to "Get good". But it's pretty straightforward to predict twitch's movements around the map, and it's not like he has a lot of mechanical options for outplaying someone that jumps on him, so the lack of mechanical counterplay against him is almost irrelevant.

And yeah, he's an obnoxiously overtuned piece of shit. This is just how you play against him, not an argument that he's well balanced.