A Nasus Balance Idea
Make it so Wither (Nasus's W) gets removed when struck by his Siphoning Strike (Nasus's Q). The most frustrating thing right now about playing against Nasus is that he can hit you with multiple Qs while you are still locked down by Wither. "You want to run away from Nasus? To bad, you're still slowed by 47% - 95% even after flashing or mobility spell."
If the interaction existed for it to be removed like consuming a mark on an enemy, like multiple champions in the game have so I know the tech already exists, he would be somewhat fair to play against.
Don't add this then add more power somewhere else, you already gave him the 50% CDR on his Q without weakening anything else on his kit (the changes to E were also a buff). So think of this as a little power being taken away as the compensation nerf that should have already happened when you launched this ridiculous buff.