Twitch out dps mages like cass with ease

why is twitch so strong? I was playing cass, I was fed and still twitch just won in a battle between his AA against my E (yes, he was poisoned), I even used seraphs shield and the motherfucker would kill me without ult, wtf is going on with adcs now? out dpsing mages by just right clicking and also having super sustain? this needs to be addressed.