All credits goes to @critical mindset from Thriller Bark forum.
This follows from three pieces of corroborative evidence.
(1) No plasma discharge
There is no electrical arc being generated from the attack onto BM like there clearly is against Vergo.
Which as you see there is a corona discharge enveloping around Vergo indicating that Law is generating a greater electrical potential resulting from the greater electrical energy/output.
The greater electrical current makes the air highly ionic and charged the creates the glow of plasma that we’re seeing in Vergo’s case but not in the other instances.
BM does not feature this aspect of the attack yet it prompts her to scream at the top of her lungs in agony.
(2) The sfx is different in BM’s case
BM is different from all these cases in that she does not feature the same sfx. All but in BMs case the sfx is the same.
In Doflamingo’s case his internal repairing ability renders the attack less effective. Law could not generate the same discharge of plasma presumably because he only had one arm at the time, and so his attack output was limited even though he had every bit of intent to maximise on the attack at that point.
(3) No exclamation marks
Even though BM was clearly in agony there were no exclamation marks I’m her panel.
Conclusion
Big Mom endured an attack that’s less lethal than all of the above, let alone the one Vergo powered through without howling in pain. Vergo was pushing Law to maximise his attack, whereas Law at this point seems to have it figured out, is not stressing it in testing out the range and efficacy of his abilities. Second time around he uses countershock it will produce a much greater effect.
There is simply a different make up of the body and mind that characterises Vergo. That much is becoming clearer for each chapter.
Pump Palace (Bonus Track)
