Maybe you want to go in a different direction with the nerf on punch through, but I think you could make some slower and opener lacking heroes far more viable if you would introduce a new mechanic:

When the target suffers block damage that would push his/her hp to 0, the attack should disable the guard. The targeted player can perform anything except blocking, when he/she moves the guard, it remains black, while the guard is still visible in black to the other players. Regaing it would take 3 seconds. This mechanic would not work if the chain only can be followed up because the target is exhausted, and immediate block

I think that some heavies would profit greatly from this mechanic, especially shugoki (though he would still need additional rework).