PG’s disproportionate advantage was productivity - despite LISPs disadvantages - which he writes about in depth here: http://www.paulgraham.com/avg.html I suspect that productivity gap would still exist because the primary productivity feature is macros, which are still either uncommon or limited in other languages:

  The source code of the Viaweb editor was probably about 20-25% macros. Macros are harder to write than ordinary Lisp functions, and it's considered to be bad style to use them when they're not necessary. So every macro in that code is there because it has to be. What that means is that at least 20-25% of the code in this program is doing things that you can't easily do in any other language.

So why doesn’t LISP rule the software universe? I presume it is because it takes exceptional skill and taste to use macros productively. I also suspect it requires a small team because everyone needs to deeply understand many macros which are unique to the system developed - deep customisation has its costs. Certainly I have worked with plenty of programmers where I was pleased they didn’t have access to macros!

PG has created two other languages (ARC and Bel) which shows a high level of skill, and perhaps also shows that LISP is not his ideal language? He wrote this about designing a programming language: http://www.paulgraham.com/popular.html and he writes about the history of LISP here: http://www.paulgraham.com/icad.html which also talks about productivity:

  if you were to compete with ITA and chose to write your software in C, they would be able to develop software twenty times faster than you [by using LISP].
  ITA's hackers seem to be unusually smart