SE stated that the nerf was due to the BLMs victory rate in the Feast, but, maybe I'm wrong, in theEU server they are quite rare.
I played some few matches in a JAP datacenter (only FL), they act very different from what I'm used to see.

Even during a Slaughter match and even if 2 GC was clashing among each other in the middle part of the arena, the 3rd one didn't start any sandwitch action,
just waited back and re-apply stoneskin ._.

It seemed that they was waiting for the LB any time to attack, and use them all together.
No one was battle high at the end of the match xD

So if they are very focused on LB people I think that the Sleep nerf was due to it, but with our pattern x.x
I will really miss it even because Freeze suck even compared to Tri-bind :/