Why does Sion's Passive have to peter out today?

Sion's Passive gives him a burst of MS. Back then this was pretty dangerous, but now it's pretty shitty. Everyone's already so used to Sion's passive that they immediately get away when he dies, and because he has to go through his "revival" animation that gives them more time to get away; by the time he reaches anyone, he deals crappy damage and moves like a slug before he dies pathetically. A good Sion can get a couple kills out of this if the nearest opponent(s) have low HP. A creative Sion may be able to make great use of this and maybe somehow get a Triple under the same conditions. However, they most likely won't be able to if the opponent's gone against Sion to the point they know what to do. What I ask, is why does his MS have to decrease before he dies? He (while having his Passive activated) deals pretty much no damage when it counts, and he's lucky to make use of his Passive in ARAM because everyone's so tightly-packed together -- let alone SR. His Q and E give him enough CC to deal with most opponents (especially if he Rs in the middle of a teamfight, which is a huge gamble that most likely won't pay off unless he and his team knows what they're doing), his W (while weak Early) is great for taking out waves of minions, and his R...is awesome enough so there's no problems. But his Passive really sucks, even though it's able to activate every death (which is actually a huge hidden disability on him, because this gets the opponent into a beneficial habit that causes the Passive to be useless). I have an idea to balance it, though I'm not including math because I don't know how the inner workings of Riot really work for damage.

Passive: MS no longer decreases during death after activating postmortem ability. Gains AD Burst that peters out while not dealing damage, but resets [to initial value with Burst included] upon using Basic Attack. Cannot use Item Actives while Passive is activated. Q: Deals less damage but has slightly longer stun (.25 seconds would be good, maybe shorter) W: Bigger shield Early Game, but less Late Game. E: Slow quickly peters off but has slightly more initial slow and a longer total slow time. R: Either 1) Same as normal, or 2) Faster and more AoE damage, but with less total range and less Stun time (to compare with longer stun for Q). Perhaps for Option 2, the Stun time could increase based on how many enemy Champs are involved in the AoE Stun (for 1 Champ, it would be pretty small compared to normal, but for 5 Champs would be somewhat longer).

I hope this looks good, but knowing the community the majority of you will find fault because it'd be unfair for you Sona mains to get Stun-locked by an AD Tank/Fighter that has enough CC to be a successful Support. I'm just hoping to find some positive constructive criticism, so for those who get Triggered from someone having an opinion I'd ask for the dick helicoptoring to be kept to a minimum. For those that actually have a sense of reason, thanks for reading and I hope to know what you think :)