Bone Armor on a 30 sec cooldown feels underwhelming to me already. The 15% damage is nice or whatever if you talent it, but that's a long ass time to wait for your only sustain without talenting into W. I haven't taken it into a real match yet, though. Just AI and Try.
Been playing Quick Match as other heroes and insta-queuing.
Xul gets decent sustain later with other talent choices but yeah, bone armor on its own isn't enough early game. And even the sustain he gets later doesn't seem like it's enough.
I have yet to play a match where his Leo-like wave clear is even an issue, so my worries about that were a little misplaced. He has almost no sustain early and gets bullied out of lane pretty easily by ranged. If left alone to a lane or being paired with Zagara, Azmodan or Sylvanas I could see Xul being a problem, like he would just add to his lanemates pressure but on his own versus most of heroes, so far, he's not much of a concern.
Sylvanas is actually a decent counter to Xul. She has better lane pressure with Black Arrow and she can bully Xul out of lane. Plus with decent positioning, Bone Prison never feels like a threat. When you get Will of the Forsaken it simply is no longer a concern unless you're playing a team baiting that talent in a coordinated gank. basically as a ranged you can chip down his health so even if he lands bone prison, he's not going to want to stay for a fight. He basically can't trade with ranged heroes, at all. Most Xul's so far haven't been making great use of the reverse skillshot though.
Every Xul in QM so far has been choosing Poison Nova which is strong, if it actually connects. It's super easy to dodge if you're not right in the epicenter. I just see this being the ult everyone avoids. It's Xul's Pyroblast/Tripletap.