Because right now she's even more out-of-sync with here theme and the lore than she was before, a massive waste of potential and the result if someone reworks as champion who had obviously zero motivation when doing this job (seriously? A passively stacking gameplay mechanic for stats? HOW LAZY CAN YOU GET?!). I wonder where in her lore Stashu has read that she was a "giant-fang-gatling-gun" - or if he even HAS read the lore or if he approached that rework from a gameplay only perspective (which, as we are reminded just recently, is a horrible thing to do). You want to know why the Sion rework was awesome? Or why GP and Fiora are good too? They looked at the themes and the lore and started working from that point, so their kits feel just natural.
But let's forget about that for a second and think about what kind of champ Cassy should be instead of a automatic-fang-gun. She should be one of league's unique poision users - and yes the poision playstyle CAN be healthy for league, if someone would think outside of the boundaries of "Poision=DoT". You don't have to use damage to have a poision mechanic. A slow, stats going down, vision fade, eventually a charm mechanic (yes seriously. Poision an enemy with X poision for X seconds and then they become charmed and slowly walk towards you. That would even work), and probably many things more you can do with over-time mechanics...
I did some thinking and thought of a kit that would suit a true poision user while also trying to keep her identity as a champion (turning people into stone, AoE , a bit skill spammy, etc.)
> Passive: Poision Affinity
> All poisions stack on the enemy. They stack faster the more different types on posion there are on the target. Cassiopaia gains movement speed around poisioned enemies, increased after a certain minimum of total stacks on target and when moving towards them. Stacks slowly decrease when not hit by a poision for X second.
> Basic attacks do not apply poision, but reset the time until the stacks start decreasing.
> Q: Neurotoxic Blast: Projectile Skillshot, small AoE on impact, deals damage and applies neurotoxin, lowering the target's vision with every stack. At over X% maximal stacks, their minimap is disabled and they no longer share vision with teammates. Hitting an enemy with that that is already suffering from another poision refunds X% of this abilities cooldown.
> W: Petrification Poision: Breaths out a cloud of poision that slowly moves towards a certain direction. This poision damages and slows. The more stacks there are on the target, the stronger it slows. At over 50% of maximum stacks, attack speed is also affected. At maximum stacks the enemy is turned into stone for 2 seconds.
> E: Acid Pool: Creates a constantly growing zone of AoE damage that applies corrosive poision: The longer enemies stand on it, the more they lose armor and resistance. Also they are damaged as long as they are standing on it.
> R: Noxian Gratitude: This skill requires a minimum of X poision stacks on the enemy to be used. Point&Click, Cassiopaia coils around an enemy and roots them for one second before stabbing the brutally with a dagger, removing poision stacks and dealing massive damage, depeding on how many stacks were removed.
This is set around an Mage/Assassin playstyle that might not excel that much in teamfights, but is brutally strong when you lure enemies into your trap, getting your stacks up on them from all posions at once before brutally murdering them in good old Noxus Style. Ya know what i mean, she did that same thing with Sivir...
Why I thought a melee ult would be a good idea? It's a bait. A bait for players who like to take a risk by getting close to an enemy despite their squishyness. They can get killed while doing this, but if they make it work the reward is some sweet sweet damage (and most likely a kill). Also her kit could need some risky elements as all her range and AoE can make her into a zoning monster.
Also like the we can see her actually using her snake body to fight (or better "to kill") instead of just moving around with it. Right now Cass could have legs, it would make no difference to her playstyle. Sure, would appear weird as hell at first, but nothing on her kit would be influenced by that - and that's a design flaw I cannot tolerate. If you create a character with a snake body, at least let them use that...
I'm not saying that my version her is perfect or anything and I'm sure a lot of people have some ideas or criticism for it, but even on paper THIS sounds more like Cassiopaia than Cass is ingame right now...