I disagree. I found his meaning clear. The core of the essay is that thinking with the right abstractions provides greater boons to reasoning capacity than comparatively trivial differences in human IQ. To make things a bit more concrete, take any game; Go, Poker, Chess. If these were truly (approached as) combinatorial problems then humans could not stand a chance at them. But over time, people have learned patterns, compacted them and shared them such that the average level of play is what masterful players might have once struggled to reach.

Lisp provided concepts captured enough structure that it cut through a lot of combinatorial complexity in the space of possibilities, making reasoning about the construction of computer programs and algorithms a lot less random.

A complaint might be he left out what aspects of Lisp provided that combinatorial boost but I'm sure many HN users could furnish those reasons. But one easy observation is the sheer number of languages and language concepts that are rooted in it. Newtonian physics is not the best physics but it fundamentally changed the way people reasoned about the world. Lisp is not the best language but it fundamentally changed how people reasoned about computer programs.

One objection one might make is that the real Maxwell/Heaviside Equations can instead be found in the Lambda Calculus/ISWIM. Despite the name, Lisp did not originally derive from the lambda calculus but just about all typed functional languages and future versions of lisp are of the LC. But a quick answer to that is influential languages like SASL and Meta Language were prototyped in and strongly influenced by Lisp (cognitive boost).