Why was Fizz given a net nerf?

Disclaimer: I tend to dislike playing assassins of any kind, so my experience playing as Fizz is not going to be as much as a Fizz main or even someone who uses him a pocket/counter pick.

Anyhow, a bit of context; Fizz in 9.14 was given two changes to his passive.

The first and most prominent in terms of visibility was the change to his damage mitigation from scaling with level against basic attacks to scaling with AP against non-true damage (remember that for later).

The second, and the point of contention I'd like to make, is that the tool tip for his ability to ignore unit detection is no longer present. I mention tool tip specifically as while the League wiki says something along the lines of 'permanently ghosted', the game itself does not mention anything to that effect.

So I have to ask; why was Fizz given this net nerf? Sure he is annoying to play against with the massive amount of mobility and safety he has on top of damage, but that literally could go for any assassin with a blink or dash as well (Talon, Zed, and Katarina come to mind), and the fact he lacks any ranged spells at all until level 6 or until Protobelt is finished makes him more reliant on all-ins to trade or snowball. And getting creeped blocked after a kill or while trying to chase a low health enemy makes him even more risky.

While the most direct solution would be just to add this caveat to his passive again (or make it more noticeable if it is still there), but I'll also suggest that, if you want the new damage mitigation to be noticeable, make an overall mechanics change to league so undefined damage mitigation matters against true damage as well as physical and magic damage. As I suggested before in other threads, the most prevalent damage over time, especially for mid laners, is Ignite, and being able to survive Ignite in trades would make him feel safer even without the minion collision. There is also the incentive for him to build off-meta if he needs to with Death's Dance; while he has no AD scaling that I'm aware of (except Q?) the healing from damage dealt (which is noticeable since Gunblade competes with Protobelt for the Revolver upgrade) combined with the delayed bleeding effect would make Fizz somewhat more durable but not necessarily more deadly.