Can we do something about Zilean's E?

Not saying it isn'e OP, but... when I W and then E again, I feel it doesn't do the full 5 seconds on my ally. I feel that they get to 1 second and then I E again and they only get 3.5 seconds of my E rather than 5 seconds. I want to know why we can't do something for it. Like on a second cast on enemy or ally: – they gain/lose 5/10/15/20/25% AS for the remaining seconds. – the E is stacked to allow it to do 6 seconds (buff the time to 3 seconds each E) – the E is stacked to allow twice the MS on allies, second casts allow 80/110/140/170/198% bonus for the remaining seconds – second cast on E on an ally allows them to be intangible for the remaining seconds; on enemies, allies deal 10/15/20/25/30% bonus damage for the remaining seconds.

The first and third seem OP, but they aren't. The bonus AS will only last up to 5 seconds, and will usually be 4.5 or less seconds. The third double will only work on allies. Enemies cannot be slowed for twice the amount.

Playing as Zilean, I've noticed that his Q is the last thing I upgrade. His E can be either really weak or very strong. The range to use the slow is 700 so he must be in range to use it.

It's just... Zilean has really only 4 ways of helping teammates. His stun, his slow, his bonus MS, and his revive. I would include the passive, but its kind of stupid at the moment; as it should be raised to 10% bonus EXP but what ever.

[P] Ever growing slow that can hit multiple enemies. bonus damage [Q] Slow and stun. damage [W] heal plus MS [E] instant travel [R] stops enemies or saves allies

[P] stun [Q] slow. damage [W] bonus armor and magic resist [E] shield from major damage [R] lift and slow. damage

[P] bonus MS [Q] lift. damage [W] slow. damage [E] shield plus bonus AD [R] knock back plus heal

[P] bonus damage [Q] slow. damage [W] bonus MS or imobile enemy slowed [E] shield plus passive or vision of enemy. damage [R] bonus health (that can revert to heal) plus area effect slow and knock up

[P] abilities cast on allies give bonus MS [Q] stun. damage [W] heal. damage [E] bonus magic damage plus slow [R] knock up plus slow. damage

[P] free spell every 5 basic attacks [Q] heal to self. damage [W] bonus MS and AS to self and ally [E] slows MS and AS of enemy. damage [R] slow. damage

[P] spells give bonuses to next basic attack [Q] damage. basic attack bonus damage [W] heal plus shield (next basic attack reduces damage) [E] bonus MS (next basic attack slows) [R] stun (buffs Q basic attack damage, W shield, and E speed boost). damage

[P] bonus MS to self when near an ally near death [Q] slow plus heal to self. damage [W] heal [E] silence plus snare. damage [R] heal to all allies

Tahm Kench [P] basic attacks stack to give a bonus to Q and W [Q] slow (at 3 stacks is a stun). damage [W] protect ally, bonus MS to self (at 3 stacks, can swallow enemy). damage [E] shield to self [R] instant travel for both self and ally. passive bonus damage

[P] Reduces time on self abilities by 2 seconds. passive bonus damage [Q] heal to self and ally [W] armor bonus to self and ally, reduces armor on enemies. damage [E] stun. damage [R] bonus AD and AP. damage

[P] gains never ending armor [Q] hooks champion. damage [W] slow. damage [E] shield plus ally comes to you [R] slow. damage

[P] 8% bonus EXP [Q] stun. damage [W] reuse ability [E] slow or bonus MS [R] revive

I also see that Zilean only has 1 damage ability. All of the others have at least 2. Just remember that.