riot basically took a steaming shit all over resistances and health. yes, youre right. its not actually worth building tanky past a bruiser build (2500 - 3k health and about 150 armor/mr), so you dont get bursted by random aoe.
in case of health its not just a terrible idea to stack too much, but outright suicide. since some genius at riot had the idea to overbuff bork and let the passive apply lifesteal.
this causes a situation, where youre not actually much harder to take down with a high health build due to the %health nature of borks damage. an adc will need maybe 1 or 2 auto attacks more to kill a 5k health target over a 3k health target. but youre actually giving the adc more ammunition against yourself. youre completely forfeiting damage for a build that causes the adc to deal more absolute damage against you and thus have a larger health pool to lifesteal off with a bloodthirster + bork.
so youre actually making things worse by stacking health, for you and your team. the adc regenerates more off you and is simply harder to kill.
its pretty much worthless to invest more than 1 or 2 items worth into resistance. instead of surviving like 1 or 2 autos more, which amounts to like a second against lategame adc, you could rather build damage and have a chance at taking the guy down. instead of being a giant practise dummy for your enemies.