If being able to clear a wave with a couple of skillcasts from range--and still be able to harass--is toxic, then nearly every ranged mid-laner is toxic.
Ahri, Anivia, Annie, Azir, Brand, Gragas, Heimerdinger, Janna, Jayce, Karma, Karthus, LeBlanc, Lissandra, Lux, Malzahar, Morgana, Orianna, Syndra, Veigar, Vel'koz, Viktor, Xerath, Ziggs and Zyra are not all toxic, yet they can all harass at range while reliably clearing waves quickly and with few casts.
Why can't Cass be allowed to do the same? If she cannot, she is not playable. She was not dominating matches, she was not ruining solo queue nor running rampant in competitive play. She was doing nothing to demonstrate her supposed toxicity. One day Riot decided she was toxic, simply by saying "guys this is toxic k."
She was dominating Treeline, sure, but Riot has repeatedly said they don't give a flying fuck about Treeline balance, so why should that have had any effect on their decision? That was her only sin: too strong on Treeline.
The rework was not only unnecessary but left her in an unplayable, horrid state that is neither fun nor compelling. She's below trash tier and she will remain so until she is either overhauled completely (moreso than Sion, even) or returned to the state she was in. "Toxic" my ass.
If they really, really want to rework her then they should've figured out a good way to do it before changing her, and especially before pushing changes that were reviled on the PBE to live. But Riot's testing process is "herp derp this is cool right??? it doesnt crash the game? awesome! lets put it in! Oh, they dont like it? Too bad! Put it in anyway and we can fix it later if we remember."
At this point I'd rather they removed her from the game and made a new champion from scratch. You can't take the fun parts of a champion out and put jack shit in its place and expect people to like it. This is no compromise, this is "fuck you, that thing you like is total shit and you're shit for liking it."