I Need Help With This Game.

So anyway with Adcs and Mages being very good recently, you know all those buffs to some cancerous and older champs in worlds patch, can anyone give me any ideas to what counters them? I'm talking about stuff like Kai-sa with mixed damage who you can't really itemize against or someone like senna who you can't really reach because she's so far away and literally hard scales because we all know no one is not building ad on her, or the insane ap dps that morde does, then there's akali one shotting you etc. How do you deal with this stuff? Cause I found out unless I am playing mundo there's really no way to survive against them and even as mundo with the ult and stuff they are so mobile and kite so well and go invisible and stuff that they can just wait our your ult while moving so fast away from you or in morde's case out heal you and eventually kill you with passive and conq. I've played some games as other tanks where i have stuff like spirit visage and helm, randuins and thornmail. Thats my core build for any ad and ap team no matter what tank champ I play and it's absolutely useless. I mean sure it does help you survive a 3 seconds on a Sej or something, but you literally would get bursted down in as soon as you engage. At that point why would I play a tank when I can go something like wukong, even though he is dog sh!t he can still almost one shot someone, has a dps aoe ult and can just run away with w if he gets caught, his passive also gives him some tank stats right.

Why would I not just pick mundo or ornn every game if my team wants me to pick a useless tank? Because really those two champs are the only real tanks in the game.