Okay so I thought this rune will be awesome to have, the one Rune that will absolutely be good, but after having one game with Jhin full build, and looking over it in practice tools, I realize that it not broken, but in fact has the weirdest scaling ever, and it sad to see this go down as one of the weakest runes to have in the game. Since it has a soft cap to it, it becomes less effective then it should be. The higher the movement speed the rune is, the lower the amount of AD/AP, this makes it have a cap all on it own, making it hard to really make use out of this. Here a link Talking all about movement speed
If you don't want to look then think of it as this, the highest movement speed you can gain without the soft cap kicking in is at 415 movement speed, since this rune is based on bonus movement speed from the total movement speed, you cant really bring this out to it full potential unless you go with a champion with the lowest movement to gain EXACTLY 415 movement speed, but even so, having 285 from unmounted kled to have that much (which means he needs 130 movement speed) he only gains 10 AD/AP, which is not much if you think about it.
TL:DR It a great rune however it in a wrong position sadly, gaining that 3% movement speed and gain profit off of movement speed was a great idea, but with the math you guys made, there now a hard cap on that rune, making it sad to make it with, even jhin awesome critical movement speed can bearly get even 22 AD, which isn't much.
If I can really say something is to change the math, reduce 8% to 6% and make it so it "raw bonus movement speed" this will definitely be effective and much better then the other method you guys made