Tanks/Bruisers? Where is the line?

So what is up with all these bruisers that solely build damage, but they don't take damage? Like why are champs like Garen, Camille, Darius, Fiora, Gangplank, Irelia, Kled, Pantheon, Riven, Tryndamere, Wukong, and especially Xin and Renekton, why is it when these champions build FULL damage, they also dont take as much damage. I obviously know that some champs have things built into their kit that reduces damage and makes them a bit tanky, but if they build full damage, they should TAKE damage. No reason that a full AD renekton can literally 1v5 solely because his ult gives him some HP, no armor or MR, just HP. Makes no sense to me and should be nerfed.

Also Nerf Ornn