Lethality can't be counter played

Why would riot buff lethality, making actually every tank in any elo above silver 5 completely useless. I work my way up to silver 1 and get shit on by full lethality ad hyper carry assassins who actually deal 3k damage a second, if there was a counter play to them i wouldnt be mad but a kha rengar riven varus or fiora can just walk into any tower in a 1v3 and just instanatly kill 2-3 poeple of there choice. building any armour at all is next to useless unless you are in turn getting 6 thornmaills, but you are still geting killed in 2 seconds from the nearly 100 lethality on them when they have runes and all of the items for it, and then when they pair it with black clever and or lord dominik's regards or mortal reminder, basically shredding through approxomitley 75% of your armour already without lethality alone. If there was an actual way to counter play other than completely changing my playstyle and stop playing the champs I like then this game is actually questionable. ESPECIALLY since you cant control who gets fed on the enemy team and if your team feeds in solo duo queue to start with.