Except Lisps that are intended for numerical work, like MACLISP on PDP-10s at the time, did have arrays. And as noted, MACLISP was around then faster than DEC's FORTRAN (an issue DEC fixed not too much later).
Lispers aren't stupid, which should be distinguished from how easy it is make a simple Lisp. Making a performant one takes effort on the scale of making any similar language implication good and fast.
I never said that Lisp didn't have arrays. I said that representing a matrix as a list of lists would not perform well.
What I meant to be saying is that Wolfram plausibly may have looked at a bad data representation for matrices on Lisp, and concluded that Lisp was inherently 100x as slow.
Lispers aren't stupid, which should be distinguished from how easy it is make a simple Lisp. Making a performant one takes effort on the scale of making any similar language implication good and fast.