The problem with Diana is her huge ratio's. Get hit with one Q, which has a 70% AP ratio, you're going to eat 2 Rs, and two balls from Pale Cascade.
So for a little over 365 mana she'll have used her entire spell list to its maximum effect and clubbed you for (75+50%)*2, 250+80%, 200+70%, 210+60%, and 440+120%. Let me put this into (moon)light... Diana was designed to be an AP FIGHTER. Not a full AP assassin.
But all of these champions deserve to be here. If you get hit with one thing, you're doomed. Diana, Yasuo, or Lee hit a Q? Well, you'd best hope they decide that they can't instantly burst you. Because Yasuo will hop right on your dick through minions, Lee will just Kung-Lao flying kick your teeth in, and Diana will pretty much get a free ult on you.
Fizz... All he's gotta do is use his stupidly low fucking cooldown untargetability and burst you, quite literally, within 0.2 seconds. He doesn't even need his Shark, but with it he might not even need to Q you. Just R and E.
Zed... He's a god damn problem. He is so simple that it's easy to tell what he's going to do, but you have nothing you CAN do other than buy one of two items:
or
.
For these 5, you gotta put in at least double the work they do in order to come out alive. To say they don't have their weaknesses is wrong:
Zed has a tough lane if you can dodge the shuriken,
Yasuo is vulnerable to poke, just keep autoing him now and then when he moves in to get a minion.
Diana is so damn susceptible to ganks if she pushes past mid-way in lane, which she does naturally because of her passive.
Fizz players, unfortunately, need our wishes and support that Chemotherapy goes well. Cancer is a terrible thing.
Lee is Lee. He has his weakness. It's his eye-sight and tendency to try for them LC$ B1G PL4YZ.