Think of it like this. IF you do 112~Swamp Hands (m) you get one hit of armor. I can't poke you.
If you do 112~walking corpse, you get 3 hits of armor I can't poke.
The only thing that blows up all of those options guaranteed is the meter burned b3. That takes 8 frames to startup.
Your -7 after swamp hands. You can backdash.
Basically, if you condition me to start meter burning to blow up that string, you can also blow me up for doing it. It becomes a game of guesses and reads because I can also dash cancel my meter burn B3 and throw you or go into a another string, but then grundy can just MB me to a 50 percent combo.
Grundy has options for every single blowup you throw at him due to his armor and properties. He is a monster of a character.
I am not talking theory either. Murphy and Dai and a couple others do this regularly.