What would you do with Glacial augment to make it fair, expect deleting it?

My idea is to change it so whenever it is slowing someone(by aas, reduction should be smaller? or items) its user will do xy% less dmg(20% sounds adequately), this way mages will have to exchange something in order to hit their skillshots. I know that they already have to build different items, but let's be real, it isn't hurting them that much. Either nerf those items or do something with rune itself. I always enjoyed mindgames and sidesteping and it's totally negated by GA. It isn't fun to run vs Ahri, Veig, Vel, Morg, Neeko, I also encountered few Luxes, Zyras, CHOGATHS with this rune.

It is removing counterplay to skillshot in exchange for what?

Do you have any suggestions?

Also offtopic, and I should probably learn this before putting out ideas. How do you calculate gold efficiency(I know basics described here, but how do you work with these scaling passives like Ludens or GLP?

If the item has passive or active effects they are only taken into account if they provide stats with a gold value (e.g. if an item's effect added a temporary flat movement speed, the gold value of this effect could be determined, because there is a reference value for movement speed). See the next section for how the base gold value of various stats is derived from "reference items".

with this, if I'll take Ludens how do I work with its Echo passive?

this post is working with old one and I would like to do the same with current one, but I just can't understand it(I'm kinda slow).

I'm stupid, but I would love to understand it, I will be grateful for every advice or any help.