The author himself says it’s esoteric

He didn't.

He wrote: 'Contrary to popular opinion, Lisp is an incredibly practical language for building production systems.'

I've read it.

It says: 'We’ve built an esoteric application (even by Lisp standards)'

The application was considered by the author to be esoteric in 2015, not the programming language.

Quote: "Our Lisp services are conceptually a classical AI application that operates on huge piles of knowledge created by linguists and researchers. It’s mostly a CPU-bound program, and it is one of the biggest consumers of computing resources in our network."

The application is the compute core of a cloud-based grammar checker with lots of complex lingustic knowledge, which generates a lot of processing load.

And "(even by Lisp standards)" just means that there are other applications in the Natural Language Processing domain, which were written in Lisp, like software to do machine translation between language or text content checking systems for technical documents.

Also, if you’re really willing to go into it you could be productive in Brainfuck. Doesn’t mean it applies to the general crowd.

It’s not a good comparison at all. Learning lisp or understanding it is a good base knowledge regardless of your primarily language. It’s not a language that’s truly esoteric and difficult to reason about by nature. Metaprogramming/macros can be difficult for those inexperienced, but not impossible. Esoteric languages are often created to either use unfamiliar syntax compared to common languages or unfamiliar paradigms to those. In the end, a lot of things are very similar in nature with esoteric languages, just a very different way, with syntax that’s not as readable as common languages. Lisp is certainly readable and easy to grin even if you have little knowledge of the language