None of the champions you listed are "naturally insanely tanky", in fact the only way they can be tanky is by sacrificing their high damage output, or if you fed them so much that they just have THAT much more of a gold/level advantage than you. Have you ever considered the fact that Diana's all magic damage/AP based, and that you should probably build magic resist against her? She's a clone of Akali, treat her as such, she does good damage and is durable, but nowhere near as much as a tank unless you fed the hell out of her early game. It's not that she's dealing insane damage while being tanky, it's that you're probably doing absolutely nothing to stop her, or just doing it completely wrong.
Jayce was just nerfed recently and is no longer as godlike as he used to be. Once again, build proper defense and he's not that bad. He's not supposed to be an easy champion to fight, as with all champions.
Riven, I really hope you're kidding. She's not tanky at all, and her shield really doesn't last that long. Have you ever seen a Riven get focused? It's hilarious, and they die quicker than some of the squishiest champs in the game because they have to be RIGHT in their face. She's is SOLELY reliant on damage, if she builds armor, she dies because she can't have that damage output she's sacrificing for it. Build decent amounts of armor early game and watch her die to every gank you pull that has even the slightest bit of cc, or just pick Malphite and laugh as she can't do anything to you. Unless of course, you feed her, which by the sounds of it, you do. I also like how you say that in theory she doesn't need boots, because aside from being completely reliant on AD, she's also completely reliant on mobility due to the fact that cc DESTROYS her.
Lol, Darius. No. I'm not going over this again.
Rengar is now forced to build tanky to survive, therefore giving him much less damage than he had a long time ago. Would you prefer getting bursted down in 3 seconds at level 1, or being able to survive the laning phase to rape him later?
Vi will not be tanky; she can build for a bit of survival, but if you've read the PBE forums you'd have known by now that she can't survive that long in teamfights, much like Diana and Riven.
People like you ARE the toxic behavior. Vi hasn't even been released yet and you're already preemptively making assumptions.
Again, Jayce got nerfed thus showing there was indeed an issue with him.
Same argument for Rengar? Are you TRYING to prove my point here?
Riven has a shield that scales incredibly well with AD, and her ultimate increases her AD. Unless I'm mistaken, the person who developed her has recanted his idea and mentioned that giving her a shield that scales well with AD is the worst idea for her.
My post is not to point out that these champions are still OP, most of which no longer are thanks to the ever so popular nerfbat... but that developing champions with these traits are bound to find a way to be abused somehow since they simply have too much going for them with too little of a drawback associated with them. I'm saying to save the time and energy trying to rebalance champions after a nerf and people are familiar with a particular play style (ie: facerolling) and simply aim for characters that have legitimate tradeoffs. High base stats with good mobility or counter-mobility kits are dangerous waters to tread. (Think what it would be like to give Leblanc or Talon the health scaling that Diana receives, or the shields that Diana and Riven get that scales off of AP and AD respectively. Disaster.)