Maybe there isn't a final, perfect Lisp. Maybe there are lots of individual Lisps that are each perfect for some class of problems. That's one of the great strengths of Lisp: if an existing implementation is almost-but-not-quite what you need, you can throw a few macros on it and adapt it into a new language that is what you need.
It's one of the greatest weaknesses too: you don't see the same willingness to say "This is good enough; let's move on to more interesting problems" that you get with, say, Python/PIL or Ruby on Rails.
If you're going to create a new Lisp (and expect people to use it; creation for the sake of creation is another thing, and doesn't need justification), you've gotta answer why it's superior to throwing a few macros on top of an existing Scheme or CL implementation. After all, wouldn't an individual programmer know his specific problem better than you do? They don't have to worry about harmonizing a variety of concerns, because they don't have to worry about other people's concerns. They could just build the language that's best for their specific problem and keep it in their own private toolbox.
This is actually what causes that disparity between what people think of new technology when it first comes out and two years later, as long as it still exists: one party was busy developing, the other party was busy coming up with reasons it can't be done, getting pats on the back for being so smart, then riding that dopamine rush to nowhere fast for two years until they meet the product again and just say "oh, I was wrong." Then this cycle continues. That's what PG's essay is about.
But being unable or unwilling to argue semantics does not make the original poster's ideas wrong. The only way to prove a determined person wrong is to engage in direct competition, and from the rear, of course, as the other party is already ahead of you. For obvious reasons, it's easier and "smarter" to come up with "logical" reasons than to "do the full experiment" to show it's wrong. We're not talking about math equations here, so a productive person's potential is more than his writing but also his skills, experience, credibility, and dedication, which can't all be ignored.
If that were true, Scheme and CL wouldn't exist themselves. Everything you can do in those languages you could have done by writing a few macros on top of their predecessor, Maclisp.
What you seem to be saying is that the evolution of programming languages has now stopped. No one ever needs to make a new LFSP, because SPs can do whatever they need by writing macros on top of existing languages. Do you realize how unlikely this is, historically? Especially in a field like programming languages, which is at the moment in a period of ferment.
If you think CL is the last word in Lisp, you probably have a higher opinion of it than any of its designers. They were in the kitchen when it was being made, and they are all too aware of all the hacks and kludges that went into it.