Why taking Ryalis off mages is a GOOD thing

I think one thing people seem to not grasp with the whole "Why are they making it for assassins" is that it got to the point where alot of champs were balanced around it, just like with Ye Olde Deathfire Grasp

Look at it this way, Xerath builds Rylais, if he hits you with his ult? VERY high chance he'll hit you again or force you to burn flash so naturally since it's such a boom to his power they now need to make sure he doesn't get out of control with it and thus he's balanced around it.

What about Azir? he was nerfed to the ground because Rylais worked SO WELL with him

Mordes? his rework was DESIGNED around it

Aurlion, if he's good with his stars you can't escape

Karthus, Permaslow W, Q'd to death

Malz and brand, slows as long as the DoT lasts

So many of these champions are balanced around this one item not to mention it gives alot of AP that mages want.

And it's not like Mages won't have a slow item, just not as good as a Rylais slow

When Deathfire was around so many mages were balanced around it and when it was removed they could be balanced based on their power alone (Whether or not Riot Balanced them well is a different topic entirely) with so many mages now not only buying it, but in some cases depending on it ( ) getting rid of it means that now Riot can look at them and go "Ok, without the slow they are this much weaker/more vulnerable so lets change these bits here to offset that" (Again, good job or bad job is a different matter)