Rebuttal to what? Measurements that yet again depend on perspective and don't take into account that Pica's palm is multiple times as big as his head?
When he have the fact that Pica's fist is displayed as being multiple times larger than his head when he holds it right next to his head, and when we have the fact that Luffy's G3, upon clash with Pica's head, has literally half the size of Pica's head.
Pica's head compared to his fingers:
Pica's middle finger is literally as thick as his head, while being 3 times as long. Which makes sense, because it depicts Pica's real body, which also has a tiny head compared to humongous fists.
Luffy's G3 compared to Pica's head:
Same G3 being Chinjao's size, who has an official height of 5m, which is more than 4 times less than Hajrudin (22m):