tldr: build mr not health
i can't find a single game where you vs a tank in lane
tanks damage output is the 2nd slowest in the game
utility supports are the only ones behind them in terms of dps
dps is damage per second
most tanks build cdr and defenses (health/armor/mr) cdr as it's the only stat that significantly increases their dps
most tanks have an ability that does % dmg mundo q ornn w maos e
these abilities by themselves don't do good damage to burst people but they are abilities most people tend to not want to avoid
as these abilities do % damage that means that when they fight healthier targets these abilities do a lot of damage
this has also a drawback and it's called resists
any defensive stats you can get against these champions significantly reduces their damage output
as tanks don't build penetration a nullmagic mantle decreases ornns damage by 1/3rd for example
this means that if ornn is able to 1 shot you a negatron cloak means he can never kill you again
but as you find yourself in this newly found immortality you get complacent and stop caring about avoiding those abilities
and thus they just stack damage
a lot of damage
a lot of irrelevant damage
also comparing a tank to an adc is a bad idea as the skill of the adc and the support of the adc largely determines their success
tanks are complete booboo in the current meta state
there is too much healing
there is too much shielding
there is too much true damage
and any kind of resists makes tanks damage irrelevant
you see that ornn beating your riven in lane so bad that she can't farm?
well she got deaths dance now and 3 points into e and ornn no longer deals damage to her in fact she is outhealing his damage even through healing reduction
your problems with tanks are only yet to begin when riot starts balancing for worlds and tanks start beating bruisers in lane again
then you will see a problem
tanks currently are at complete mercy of their teams
and as you said yourself git gud