"Deep" Item Counterplay

As in there isn't any. Exhibit A: Only response for ap to deal with a tank is building , but it gets completely cancelled out by . So what's the ap supposed to do?

Exhibit B: You're fighting against an ad assassin who focuses on building lethality items. So you build armor to counteract the flat pen. So then the ad just builds , or and that's the end of it; armor becomes useless.

Why are these "counterplays" so one sided? Tanks building is hardly off the beaten path of what they'd ususally build with health and mr. And ad's building just prepares them for late game against tanks. There's no answer, no back and forth, for when people counter build. It's just: build this to defend against ad threat > ad threat builds thing to cancel defense > defender has no chance Or: tank existing is threat > ap build only thing to answer > tank build cancels ap only answer > ap practically useless

I understand with ap vs tank at that point the ap focuses on the other enemies and leaves the tank to the others, but that doesn't really asnwer the problem of lack of counterplay in items. I also understand that against an ad assassin who is getting ahead you should avoid at all costs, but the assassins have ways of diving past the frontline or the fact that ambushing exists, so again the lack of counterplay in items isn't addressed.

I understand items can't do everything for the player, but it would sure be nice if builds weren't stagnant, or at least felt like they weren't useless.