Tbh Twitch is just one of those champs that will either be completely useless in your game and be killed as a minion or will 1v9.
Completely depends on his support and team mates and of course on the enemy as well, if they have a lot of immobile champs then he's really good, on the other hand if the enemy team has something like Zed,Xin, Kha,Rengar or any assassin/diver while Twitch has brand supp then it's going to be a really damn tough game for him.
Thing is his ult gives him a lot of AOE and Range which people will consistently moan about, but at the same time if he stays at a long range then he can't shoot multiple enemies, also his enemies can easily walk out of his range or just avoid his autos since they turn into projectiles, that's why ironically twitch deals the most damage with his R when he's close to the enemy team and can hit more of them, but this usually ends up with at least 2 flashes on him and a hook.