Warmogs + Stoneplate is honestly overpowered.
It shouldn't be a common strategy to rush warmogs + stoneplate and just facetank an entire team, then burn a gap closer or flash to get out, and just wait to regen all of your health in a few seconds, then re-engage.
Rinse and repeat.
You should not be able to just zerg your way through an enemy team by going in and going out using warmogs.
Its actually garbage.
Especially with how much damage tanks can do while building full tank items and zero damage.
They need to up the amount of health required to get the passive, or increase the out-of-combat requirement, or decrease the health regeneration.
I should not be able to exit and re-enter a fight 2-3 times while still dealing meaningful - maybe even threatening - amounts of damage. That's just bullshit.
I'm sejuani. I charge in, I proc my stun, I deal MASSIVE damage, I CC the hell out the enemy team.... UH OH.... I'm getting low! better Q out to safety!
a few seconds pass....
Ok cool, I'm back to full health, time to go back into the fight that's still happening and continue disrupting the ever loving piss out of the enemy team and soaking butt-tons of damage for my team, while being an un-ignorable source of damage until WAIT.... I'M LOW AGAIN! Better exit the fight!
Oh phew... I'm full health again.
Same with zac, nunu, and some others. Really, anyone you feel like building warmogs + stoneplate on. Doesn't really matter who the champion is. This item combination is cancer.
Shouldn't exist if tanks are allowed to do as much damage as they're currently allowed to do.
alone going to give you enough health to activate its passive. (maybe if you're 
)
2: If they rush those two items they are nothing but team fight tank, if they're separated from multiple enemies the resistances from 
get cut in half.
3: most Pure tank champions get damage from item stats like 
or CDR. While warmogs gives 10% CDR it that alone isn't enough to really grant much bonus damage
4: no mana
5: I still don't know why people think pure tanks deal damage. Maybe to an ADC, a champion who builds NO defenses, but if they get to an ADC that means either no one protected them, or they where caught out. Which is their own fault at that point.
6: you know you can body block a Sej Q right? (it doesn't even deal damage compared to the rest of her kit)
7: 
... damage? maybe early game, but that's a stretch
8: Zac is literally made to be a diver who gets in and out of fights, so i guess that argument is fair, but that his thing, taking that away would actually gut him.. (like literally read his entire kit and tell me its not to re-engage multiple times)
9: If you focus enough damage on the tank during fights to bring them low multiple times you're playing the game wrong my friend.