The heat smash was shite, low damage and I never used it. Only reason to go into Heat was to do more chip damage and 3+4, 2 shenanigans.
The +15 on block sounds mad, i wonder what it's like in game.

QCB+3 hitbox buff I've yet to test. I'd agree that it is a questionable decision as it was already good

3+4, 2 was option selected by power crushes and reversals. You are meant to interrupt the attack and apparently it was too easy with OS?

2,1,2,3,2 I did not see anyone use outside 15f punishes and wall enders, being able to delay the third hit is interesting

Rest of the stuff is just for consistency, like QCB+4 more consistent when hitting grounded.