13.20 preview has milio changes (which are kind of under the radar relative to big jungle nerfs and snowball nerfs):

Shield increased 60/85/110/135/160 >>> 60/90/120/150/180

Recharge time reduced 18/17/16/15/14 >>> 17/16/15/14/13 seconds

In general, the point is a cd going down 1s matters more the lower it is.

So in terms of total shielding over time, going from 18 to 17 seconds means less than going from 14 to 13. For example in 60s 18->17 gives you 60/17 - 60/18 = 0.20 more shields, whereas 14->13 gives you 60/13 - 60/14 = 0.33 more shields. So reducing it 1s from 14 to 13 gives you a .13 greater boost to how many shields you get per minute.

Another example of this is a while ago riot decided people should play lulu more and lowered her W cd, making W max lulu super strong until it got nerfed.

Now combining this with Milio shield going from 60 to 160 to 60 to 180, they must want people to start playing him again and max E. Whether E or W max actually is or will be better, I have no idea.

Really this verges on pointless nerdiness; just play him after the buffs and see how it feels. Still here's a graph with how much HP he currently shields in 60s, how much HP he shields in 60s after the shield increase, and how much HP he shields in 60s with the shield increase and CD reduction.

Here's the current E rank 1-5 shield HP per 60s (red), E shield HP per 60s after 60/85/110/135/160 >>> 60/90/120/150/180 increase (blue), and E shield per 60s after the increase and cd 18/17/16/15/14 >>> 17/16/15/14/13 (green):

At rank 1 the buff is 200 to 212 shield per min, whereas at rank 5 it's 686 to 831. Ofc as you reach late game all numbers are higher, but still just so you can see the effect, plus it's only lvl 9.

Also milio gets 2 charges idk that probably matters too but whatever.