Sylas is the kind of League of Legends champion that appears quite difficult to balance. He is either overtuned and unbalanced, or completely weak because of low values.
However, it doesn't mean Riot just gave up on him, and they certainly proved it with the balance change he underwent with Patch 10.1.
Sylas is both a Skirmisher and a Burst, and the changes he received clearly aims at increasing his tankiness and damage while reducing his overall lane control. The intention was crystal clear: shifting Sylas from his all-rounder status to transform him into a late-game threat.
It appears that Riot felt that these changes weren't actually enough.
This buff could be an overkill, especially regarding the fact that Riot Games is clearly aiming at making Sylas better for high elo ranks. At other ranks, he could become the new Akali, and suffer from permaban.
These changes will be shipped to the live servers tonight, so the question remains until at least tomorrow.