why is armor so useless vs ad assassins?

you can be a 10.000 hp sion with 500 armor yet a zed or yasuo or xin or yi clean the floor with you. and i understand when you say yi and yasuo have true dmg, but what about zed and xin (without conquerer) how is it that they just destroy you?

i think without ANY ad assassins the game would be 100 times better. ofc not for those edgy assassin only players.

also arent assassins supposed to be like "high risk high reward" didnt riot state assassins go in, take 1-2 ppl with them and then die

no its actually more like this: they go in, fuck 1-2 ppl completely in less than 1 second and then use their w to shadow out, or their r to run out or their e to dash out etc etc

"well then cc them" yea its so easy using your entire cc ON ONE ENEMY when he penta's your entire team with an entire combo. wow we used ALL our cc to kill that 1 assassin. oh shit we're at 100 hp and have no spells left, guess the 4 enemys can afk faceroll us now.

and to all the ppl disagreeing: tell me what im supposed to do vs ad assassins? you cant just say "no they are balanced" and yet not be able to provide any sort of counterplay.