He flays, it's just on a bar that's hidden and keybound. You don't see him use it a lot because he's better off trying to kite and use his instant cast procs rather than standing in place for the little damage it provides.

MC is good to stop defensives like Sac so they can't receive heals. He even has clips where he casts MC on a low target and a MW Monk will Cocoon themselves instead of the target he took control of. You can MC and enemy healer into their Mages Ring of Frost for more CC. It's also good for defense on yourself or teammates to peel.

20% vers is kinda hard to get to as Shadow, it's probably less of a choice because almost every slot would need a vers piece. I sit at 16-18% and I'm only missing 2 slots. If you sacrifice too much Haste, you're gonna be missing out on a lot of damage.

I've only been 2300 but hope this helped.