Interacting with enemy laners mid isn't fun (when you're not an assasin)
**I don't think Fizz is OP, for example, let me make that clear right now. **
However, it's kinda annoying that at lvl 6 even a really bad fizz will 100-0 me with his ult. How do you even dodge that ult anyways? Specially as an immobile mage like Karthus.
Same with Zed, Talon (and btw I play talon a lot), Kassadin, Leblanc.
My last game last night, I played versus a Fizz who I could tell was significantly lower skilled than me. At lvl 1, I brought him down to 10% hp with poke and I had a CS lead. Soon as he hit 6, I couldn't be in the same lane as the guy anymore.
I still won the game but damn...how is that fun? What makes you think I want to interact with my enemy laner when the only possible outcome is that I feed? What I got going for me is waveclear and late game scaling, so of course I just want to push and roam (or freeze).
So the mage mana nerf is pretty unnecessary and frankly BS.