So what doesn't Sylas have ?
Not even saying he's broken or whatever... I was just looking at someone playing him and he literally has everything in his kit. AA enhance, shield, healing, slow, knock up, mobility and not to mention that he can steal your ult so he's basically a better version of your champ if he steals your ult.
I don't see what's the weakness here ? Why shouldn't you pick him in every situation ?

those are some champs i play and ... i dont see a reason to CC those in a team fight compared to say an assassin or a yi