Lee sin is an example of what CoC in the cunning tree could do for the game
for a long time now lee sin has been kindof strong/ why? Part of it has been that he's had the combination of shields, attack speed boosts, mobility, and sustain. Its in small amounts that are difficult to nerf individually but at the end of the day he is a little overloaded even if he is balanced or isn't whichever
But back to the point, when lee wants to move lee can move and he gets a little shield along with it. His AS steroid lets him evade more damage by being rooted less by his own autoattacks. Sustain makes him feel tanky when he is dealing damage and scales with defense better than a shield does but he also has a shield which in a game where the % hp you have left is actually kindof a big deal for how much damage others deal to you is itself a big deal
When lee sin hits you his max hp actually rises in a way and he will be moving around quickly if he can't just burst you right away.
When lee sin runs from you, he gets a shield that doesn't care how much damage he actually dealt.
If he can't tank enough he can kick you away thus creating another form of evasion.
What I'm getting at here is that evasion needs to be looked at and should be looked at in a different way than normal defense, its just like with the stealth issue and the incalculable "information advantage" which shields also give since you can actually see faster exactly how much damage you'll be taking before you even take any.
these champs all get shield based do-overs until they finally catch you with your pants down which would explain partly why they wreck your shit in low elo but not so much in high elo
But keep in mind that the shield vs the nature of the ability used also matters.
these champs have alternate evasion forms but ultimately its the combination of evasion and mobility that really makes it scary.. but add sustain and they start to feel tanky as shit even though you know they aren't really that tanky
here are some cases where regenerating shields done the wrong way have caused some issues that could also be part of the solution. Multiple but very limited shields on champs like
and others have shown themselves to provide limited but actually very interactive gameplay that probably wasn't really balanced for these champs.
Instead it was meant for champs like 
or 
who honestly could use a % healing buff instead of a bigger shield on a longass cooldown for them to situationally abuse the shit out of to the point they will probably get nerfed. Instead we can have a or even 
getting shredded by 
and getting a second and 3rd chance to engage because he can resist penetration or true damage or something.
btw the new champ will have a shield with a purpose similar to what I'm describing and it will be based on who she attacks rather than who she CC's and apparently its working fantastically on the pbe, maybe a little too well before her tuning but the point is that this could be used to shave and shift power on things like assassins and melee carries for a healthier gamestate.
And yes, it would mean that lee sin would be changed and probably in a way that would afford him a lategame. Imagine extreme shielding in the jungle because animals attack too slow or whatever or getting shielded based off enemy attack speed.
TL;DR
lets look at evasion and information advantage from shields differently
btw another form of information advantage shields give is that for the most part you aren't going to know exactly when they are back up. You will know how much hp a player has even if you don't necessarily know their effective hp. But that's one more issue to solve for clarity.