He's an AP fighter right? Usually fighters build a damage item, say BC or TF, then into either a defensive damage item like Sterak's or Tiamat then pure defence, with SP, Deadman's, stuff like that. Sylas current build is pure AP. Nothing like the AD fighters that exist.
Unreal healing with AP scaling, dash shield, area of effect slow, area of effect passive autos, every ability works as an auto reset. Not only that in his ult he is given compensation in the form of an AP scaling if the ability has no AP value. He makes 200% more use of Renekton's or Trundle's ults as they have AP scalings but they don't build AP, yet he takes Caitlyn's and it adds an AP scaling to it to compensate him.
Here's what I'd do to change him plus an extra.
- Make him about level Q first for waveclear and poke (should be already but give it better base, less scaling).
- Change his heal to a % Max HP. He's a fighter right? Darius, Illaoi and Gragas healing is based on % HP, whether missing or max. This will encourage him to build HP as a fighter instead of his current AP melee mage.
- Reduce the ult stealing to 250% cooldown of the stolen ult. Make him about stealing ults at the right time and using them at the right time, not oneshotting an ADC with his base abilities, that's an assassin.
- Introduce a new AP fighter item:
+
+
+ 650g = An item with 50AP, 300hp, 40% attackspeed, 5% movement, 20% CDR and Wit's end's old passive. Make it about long drawn out fights, not burst.