how good is twitch atm?

In the laning phase, he might just be the weakest ADC. However he does bring unrivaled pick potential with his stealth in the mid to late game and is one of those carries that can obliterate an entire team thanks to his ult. Positioning is a prime concern considering his stealth is an unreliable escape and he does not have a dash.

Think the risk of picking Twitch is what scares people away from him considering his rough laning phase and lack of escape. The upside of Twitch is fantastic though. Overall, he is probably in as good of a spot as he is going to be in barring indirect changes that benefit and would likely get him nerfed afterwards.

Twitch is viable right now; he is probably Tier 2. He's balanced for the most part he doesn't have significant advantages early-mid game which makes him unreliable in solo queue. But I've had a good amount of success with him in solo queue, if you can lane really well and get gold on yourself you can easily carry, it's just there are currently better adc's for doing so such as Corki, Lucian, Jinx etc because they are stronger early game. But in LCS, and any Team based 5v5 yes Twitch is very viable right now.

Good enough to be the world champs main adc. He's still extremely strong, you just have to survive laning phase and not try to ult inhibs and the nexus down and realize your ult doesn't hurt them because of a bug that's been in the game for years. Towers are fine though ;)

Twitch needs a lot of game knowledge, great positioning, mechanical skill, team coordination and support, which is why you see him in competitive play but don't see him much in solo q. You can probably get away with him in solo q, but he's no Lucian.