Where are the people on the mastery curve of Sage players this patch so far? What was her pickrate before the patch? Is it possible that your nerfs scared away the less-skilled Sage players?
This is our current suspicion, but we want to give it some more time to breathe before digging in this deep. But yeah, her playrate has gone down a chunk - so if I were to guess, it seems more likely that the "autofill" less experienced Sage players are picking her less on this patch due to the nerfs, and more experienced Sage players are sticking to their guns, making the nerf seem less consequential then it actually is.
We'll have to see how it plays out over the next few days and then assess the Sage population at that point. Good intuition on this!