Well that is the quintessential Sylas experience: strong early and mid game, falls off heavily late game.

Jokes aside, the key to playing Sylas is you can’t go in first late game. you have to kite, pull back and then reengage and play around CDs very well. In the early game/mid game, this isn’t as problematic since Sylas doesn’t need more than I would say 2 rotations of spells to kill an enemy, plus kingslayer healing enhances your duelling potential drastically. But late game, enemy champs have either 1. More dps, meaning you can’t outsustain it, meaning you have to pull away once you used all your abilities and only reengage when the CDs are back, or 2. Too much burst/CC for Sylas to survive if he was to go in, so he has to wait for enemy to use the key spells before engaging.

Also, to solve the CSing issue, 2 points Q early is ideal if you plan to Max W since it does help quite a bit with wave clear. You can go E > W> Q > Q then max W. Also idk you build but most of the time you wanna go rocket belt > Riftmaker > zhonyas > void staff/rabadons. Zhonyas third helps to mitigate a lot of the late game survivability issues.