Alright i'll agree about Acno. PiS is what made him that ridiculous, just like FH Zeref. Because yes, FH Zeref if doing things properly would have let zero chance to Natsu. Unfortunately, in the manga a huge amount of PoF and Pis were in that fight, and keep in mind these are restricted in the tournament. August isn't gonna sit around letting Natsu punch him.
Anyway, about the ABC thing. B had an unlimited amount of power, that's right, however did his last attack (a mere punch) become unlimitedly strong or something like that? Not at all. At the end of the day this unlimited supply of magic didn't get anything done, aside from reversing himself when his body got owned.
August doesn't have an unlimited amount of Magic Power, but he doesn't need this, because he has the ability to copy and negate Natsu's magic, which is something Zeref couldn't do, FH or not. So no, my point still stands. Natsu's victory doesn't matter, he can't use his magic against August.