Because IE deals true damage, Conqueror deals true damage, we literally have a true damage steroid in every game.
Seen a Guinsoo yi? He tanks, and shreads tanks. Crit dark harvest yi? 1 shot. Assassins are starting to feel redundant in this damage steroid meta. Why play a champion with a bunch of tied in condition for a 1-shot, even when fed?
Talon got a huge chunk of his damage now tied to his auto attack reliant passive. Zed needs a couple seconds to kill, which can be negated with shields/zhonyas. Dark harvest Yi 1Q AA for a kill (granted, you won't be pulling this in high ELO, but atm, I'm doing some normal games with DH yi. Alpha - kill - Alpha - kill. There is no counter unless you zhonya or build at least 2 tank items - not feasible on lots of champs). Then there's stormrazor wukong, successor to lethality wukong. Leesin is also a no-counter assassin, if he meets his damage threshold, due to Q R Q E stun lock, and high base scaling. Riot succeeded in giving assassin more counterplay, then introduced so much damage into the game, that turns any burst bruiser into an assassin. These may help introduce more kills into higher plays (which I suspect is Riot's goal, to make championships more interesting with high risk high reward plays), but it turns lower elo into an absolute mess.