Someone explain the role of tanks to me

I'm just a bit dumbfounded because I have always been under the impression that tanks are the front line. You know, non-damage dealing, damage absortion & being the utility providing part of a team but they succeed in all of those areas while dealing absurd damage, which is why I always get pissed knowing that the sole reason I have lost a game is because one champion refuses to die but yet pumps out damage equal to that of a carry or burst damage dealing mage. Tanks are supposed to be weak early game but I have yet to see that in a lot of games I have played, in fact I find that it is quite the opposite. They remain tanky very early on with high base damages & what seems to be even better scaling that other champions. Take for example, Morgana having her Q AP ratio reduced to 75% from 90% & nautilus having his Q damage buffed to 90% from 75% (in recent pbe notes). Honestly why? What's with the damage? Mind you this is happening all the while having tank items provide defensive & offensive stats & being some of the cheepest items in the game across all roles aside from support. Then people want to get pissed at Vayne because she does a lot of damage & %health health to top it all off. I'm no fan of Vayne myself but if I were to main adc why wouldn't I pick her? Tanks are a nightmare because of how they function in league, so I'd want to deal with them in the most efficient way possible, but alas, here we are with Amumu, Nautilus, Trundle, Sejuani & of recent Garen - (this fucking prik of a champion[I really hate this guy]), all recieving buffs towards their damage output? This is along with Thornmail & Bramble vest having their passives buffs as well... It's as if the balance team make these changes & then go on to play a completely different game while they wait for feedback that they won't pay any attention to.

There's so much else that needs addressing like Riven, Yasuo, Spear of Shojin, Vladimir etc. Still they're just ignored while other unnecessary changes are made, like nerfs to Morg mid & buffs or tinkering with champions that just DO NOT need attention, at least not right now i.e. Fiora, Jhin & Camille. Urgot just got out of meta, sorta after being a top pick for the top lane because he was broken af, now that a few changes have hit him (that in fact actually haven't done much to how strong he is), people are reverting back to champions like Yorick. An unrelenting braindead splitpusher with an ult that makes it feel like a 2v1 everytime you attempt to fight him or prevent his inevitable push. I just find it ridiculous how all these tank champions continue to be as broken as they are and face little to no consequence. Then you find Zed / Morgana getting nerfed...

I was previously thinking to myself that people should give the balance team a break but after all this time I finally agree with the rest of you screaming your heads off at the balance team that know jack shit in how to make an equilibrium semi-possible for the game that is League. JFC.