Hello, sorry for bad English.
I play league not that much, I try Sylas and completely love the champion. But i play top lane, not mid, and with nerfs on the shield that give you only magic damage defense it so hard to win lane vs all bruisers and Yasuo's.
Because he melee champion, and you had to farm in close range and fight, like Rumble, Shen, Mordekaizer. And Rumble, Shen, Kaizer has there shield that block all damage to deal with this problem, but Sylas for some reason don't.
Another aspect, that in team fights again you as Sylas have to face tank tons of damage to be able to deal damage, and without protection you die so fast.
I know, that Sylas has crazy life steal when he low. But this ability is long cooldown, and you need to be really low to proc it. For example Mordekaizer, again melee champion has his shield from ALL damage, and Plus heals from it. Yes, Kaizer and Rumble don't have gap closer like Sylas, but they have slow and pull to you, on top of that they build tanky items that give them health. If you build health items on Sylas he deal like negative damage, you start basically heal enemy team with your hits.
So i hope you bring the attention to one of the lovest win rate champion in the game with some buffs to play him in more roles that mid lane.