he has to have some glaring weaknesses if he is going to have times in the game where he is a monster. Twitch is basically a really well designed kit in my opinion. he has a strong identity, and come late game might be the best ADC in the game if you factor in his massive range and piercing bolts. when it comes to a late game team fight theres probably not another ADC you'd want. But if you made him strong early he'd be the only ADC chosen. Keep in mind, Twitch has some of the best attack speed scaling in the game and a massive attack speed steroid in addition to a range and AD steroid. He feels weak because until he levels up he truly is. Until he gets his bork he is pretty underpowered, but I feel if he never had a time in the game where he was weak then he'd be one of the more obvious choices for ADC. Hell even WITH These weaknesses he is still good if built around. He also can feel weak because twitch really relies on his support to make plays due to his low range without ult and lack of play making ability outside of his stealth which is usually suicide if you initiate early game with it. Twitch's sacrifices raw flat AD burst crits for massive attack speed scaling and team fight power unrivaled by any other adc. I'd say the only ADCs in his league for team fights are probably Jinx and maybe MF if you get a perfect Ulti. He isn't quite the single target burst of say a vayne or kog maw come late game, but if the enemy team is clumped or locked down in a line by CC, twitch can singlehandedly win a team fight. Hell even without the CC he can win the fight. Twitch is STILL very good. he just relies on a good support thus making him not good for solo Q, and I feel he's not playing LCS solely because the meta doesnt favor his mid game spike from before. Where last season you get bork, roam around and blow up squishies, he can't really do that now because of how tanky teams are. sure, he could still make a play mid, but if enemy jungler shows up he isn't going to be able to melt through them like before when squishy was the meta. twitch also benefited from being able to melt the entire team with his ult. with tanks being very meta right now, even with his ult, he isn't going to be able to do what he once did with his ult and shred the entire team. He is still a great ADC in my opinion and the best team fighter, but there's just some reasons why he's not being played right now. I dont feel he needs buffs or nerfs. the ONLY thing that bugs me is that twitch's main damage mechanic is his E capping at 6 stacks with Kalista having infinite stacking on basically the same type of ability. However raising the cap(can't have it be capless) isn't viable because of his passive. if you could endlessly stack his passive, he would be op as his passive deals a ton of true damage over time once he gets later in the game. possibly giving his E a slow or something else would be nice, but I'm not sure he really needs much of anything else. He's in a pretty good spot imo
at least 
and forced her to spam e they nerfed 
but then he's still playable the removed 
silence but he can still win against mages unlike 
but she roams better then him since she has no mana cost and her ult is not her source of mobility