What people don't get about tanks in League...or gaming in general
Without getting too preachy, so I can get straight to the point: Just because you're tanky, doesn't mean you do no damage.
Yeah, in many MMOs, the tank class usually has very low damage output, but the damage output of tank classes in games varies depending on the game. For example, in Etrian Odyssey, a franchise I love to fucking bits, it's a turn-based game where the tank class characters don't just do "very little damage". In most instances, outside of the latest entry, they almost always did literally 0 damage in fights. Like legit 0. None. Nada. You didn't even use them to attack in most cases. ALL they did was just shield and nullify enemy attacks. Meanwhile, in a game like Pokemon, a turn-based game we all know, some tanky picks are like Clefable, where they don't fight that hard, and others are like Snorlax or Mudsdale, who provide a way stronger offensive threat. Hell, in Bravely Default, nearly any class had the tools to push their damage to the damage cap with the right setup, which included the tank classes, although the dps-oriented classes could achieve this easier.
The point to be made here is that how much damage a tank deals in any game that utilizes the concept of "classes" is based on that game itself, not some "general rule of thumb that tanks should never hurt you". Laning still exists. The fact that you, as a squishy carry, didn't build any defenses while someone's bopping you with skills that are steadily getting stronger with game length while they rank those skills up is still a thing. It's not like the damage of tanks scales THAT well into the late game, save Cho'Gath. It's not like tanks like Poppy are always going to paste you onto a wall and beat your face in. However, you should respect the fact that, hey, ultimately, tanks in this game don't just buff defenses and stand in front of incoming attacks. They also fight. They also deal damage. If you don't respect them, and they're playing their cards right, yeah, they're gonna end up killing you, just like how you were going to kill them.
I keep seeing all this "tanks do too much damage" nonsense...and it's nonsense. Legit nonsense.
is a cc machine (isn't a tank tho).
fit in the true tank category. He just blocks everything and slows people. Never tries to hurt enemies just defend against them. I also feel like 
fits in the just cc and tank category as well.
and 
(who mostly will build some ap these days) no other tank in league has taunt. So, if they all had 0 damage, they would be completely useless. If someone who posses no threat of damage stands in front of you, you can simply ignore them, so people would just ignore them completely and go for their back line. The damage they have, albeit low compared to a dps, is enough for someone to consider them a threat and turn on them when they have no access to the enemy back line. Also, someone with absolutely 0 damage has no means of defending himself in a 1vs1. Every time an enemy would appear in front of them, their only chance would be to run away.
without penetration against a tank like 
with 350 armor and an 
, the ADC will barely scratch her, especially considering the HP pool of the tank. But the ADC has zero defenses, thus Poppy needs no penetration, whatever damage she will do will be mitigated very little, and with the low HP pool of Varus, even low damage will hurt. Poppy wont think twice before jumping on him.
as soon as he is in, which will further reduce his damage.
, they will have a hard time trading damage outputs because one has defenses that mitigate the others offense while allowing that defense to provide a huge offense.
it's donezo.