Note how Shisami gets no introduction in that script. He just shows up out of nowhere in the battle. He's presumably one of the mercenaries the script mentions right before him but it's not even outright said.
In order to "fix" that, they added him to the earlier scenes of the movie to introduce him as one of Freeza's elite. It seems like no one noticed how pathetic that role, and specifically the Zarbon line, made him appear to be though. But, yeah, it wasn't Toriyama's fault, it was Toei messing up.