IF i rush thornmail I shouldn't lose a fight against 1-2 ad

if my first item is thornmail. and I just completed it so it's like.. 10 minutes into the game, I should not be fucking losing to ad especially when the enemy team picks 4-5 ad. cause when can I even build mr at that point??? I feel like I'm facing too many teams that have 5 ad. nocturne, yasuo, tryndamere/irelia, marksman and then pyke.

AND RUSHING ARMOR DOES FUCKING NOOOOOOOOOOOOTHING like it used to. rushing 100% armor should make it so you don't die until 25+ minutes against only 2 of the enemy team. armor is supposed to make u tanky. ad scales late game. armor should counter ad early. this is my basic premise

when I have 3 armor/hp items by 25 minutes and can lose 1v1 against an ad THERE IS A PROBLEM

it never used to be like this man.. I used to rush thornmail and I wouldn't lose a fight