I feel like fireball is a good way to throw people off in the distance who just neutral duck in anticipation for a teleport. Does decent chip damage too. Some times they jump after second guessing themselves which leaves them open for a teleport or spear. As far as demon breath, I find poking into it is effective. Some people don't anticipate it being amplified and it seems kind of difficult to punish in certain ways due to the push back.
But yeah, isn't the whiffing issue of misery blade 3 character specific?
I think Kung Lao is a culprit. B1,4 MB3 hits on many characters consistently, but a few whiff consistently. Idk why NRS wont fix it.