If I could make my own language and stack, I too would be mega-productive. However, others likely wouldn't like it and be confused by it, even though it's dirt obvious to me. Roll-your-own has limits. Sometimes 2 or 3 like-minded Lisp developers connect and roll for a while, but over time they will find it a lucky match-up that the real-world can't repeatedly recreate. Lightning in a bottle evaporates easily.
The bottleneck of "paycheck" programming productivity is communicating between human beings, who may shift over time. Cranking out compact code fast is secondary to this. Program for people, not machines and not cleverness graders.
Cyc is developed by a team since the early 80s. Reduce since the mid 70s. The SBCL and CMUCL Lisp implementations come out of the early 80s. Maxima has its roots in the late 60s/early 70s. The commercial Lisp systems from Franz and LispWorks are developed since the mid/end 80s. ACL2 (a theorem prover used in the chip business) comes from the early 90s. ITA (now Google) started mid 90s. GNU Emacs is from the early 80s. Autocd/Autolisp comes from the early 80s. PTC's Lisp-based CAD system (with a few million lines of Lisp code) must have been originally 2000 or earlier...
There are also a bunch of examples where Lisp was used to prototype or for rapid application development. This enables exploring ideas or conquering early markets. Later iterations may then reimplement the thing... That's another model and is also fine - though there are projects which had not much experience and were not able to get the thing off the ground. For example the first version of the Postgres database was written in a mix of some Lisp implementation and C. This did not work well for them and they switched early away from Lisp. Similar the first version of Reddit was written in Lisp, but it did not really work that well for them and they switched to Python.
> The implication often given is general purpose productivity superiority
I don't think that claim makes sense in general. Much of the productivity in modern software development does not come from the programming language. Much more important nowadays is the general eco-system.
For example it makes very little sense to develop apps for iOS in Clojure, since there is zero support for it from Apple. Thus most iOS applications are written in Objective-C and/or Swift. An assumed 'general productivity superiority' doesn't help at all to compensate the total lack of platform support from the platform provider.
I meant for "general" programming. I apologize for not wording it clearer earlier.
Re: There are also a bunch of examples where Lisp was used to prototype or for rapid application development.
Yes, this is a niche it often does well in. It's partly how Paul Graham beat competitors in the store app arena.
The post you responded to specifically used Java as an example, though. Clojure specifically is clearly targeted as an alternative to writing raw Java. A number of other languages rushed in to compete for that space, and while Scala and Kotlin seem to be more popular than Clojure, I have to admit the only JVM app I actually rely on now, uses Clojure.
Puppetdb, specifically. Puppet is a ruby project, but the database component is written in Clojure. I dislike Puppet for many reasons (syntax, coupling, architecture), but not because of its database backend.
Their code was never touched by those who stayed and were able to work together. Later it was rewritten, because in spite of tons of unit tests (which passed), it was full of bugs. The code was considered "write-only". The rewrites averaged at 5-10% LOC.
In 2017 a customer wanted a set of services written in Clojure. Based on their Java experience they wanted to hire 10 devs. When I arrived they had 4, over the 1.5-year period I was there, they hired and fired 4. When I left they had 3. All 3 were not experienced in Clojure prior to the project (Java), but by 2018 each knew the entire codebase and was able to modify it and able to step in for each other. They spent less than half of their budget and all goals were met ahead of schedule.
IME learning how to put Clojure and its ecosystem in good use takes more time and effort than other languages, but its effectiveness really compensates.