A skilled operator can shoot a pump just about as fast as a semi-auto.
Paul Harrell addressed this issue.
https://m.youtube.com/watch?v=fDnyRXF_0Ck
He’s still slower than my Saiga or a Benelli or Beretta, and when you run a pump that fast you always run the risk of short stroking, which takes your gun out of action. The big problem is that even if you can somehow run your pump as fast as a modern design semiauto, you still run into the problem that once you run out, your reload is very slow. In the time it takes him to stick a loose round into the chamber, I’ve already swapped mags and am firing again. Yes, there are mag fed pumps, but they’re rather kludgey.