I see what you mean Ion that of course they benefit from the passive, however junglers in this time are mainly about ganking which diminishes the overall effect for a jungler, and often you might find yourself to die a lot because of how easy a target you are thus ending the benefit from your passive while you're dead. But regardless of that, compared to many other passive in the game that other AP mids possess it is underwhelmingly UP.
Thank you Shinmey I had a look at your thread in the past and found it interesting for the possible changes it could bring, which were needed to TF.
Regarding the E proc I noticed it too, and I think it is for one reason, the game calculates whether you can slay your opponent with W or not. If you can E does not proc, whereas if you can't slay the opponent/minion without E then it procs. It might be a wild guess but I observed it for a while and it seemed to behave like that, I might be wrong.