On the other hand, they allow you to do some very interesting things like using specs for complex validation. Once written specs can be then used for generating data for both - UI testing and property-based unit-tests. We once have build set of specs to validate an entire ledger - imagine having to be able to generate a bunch of transactions where numbers intelligently build based on previous entries.

Other languages even though have similar capabilities, like type providers in F#/OCaml, zod in Typescript, quckcheck/scalacheck in Haskell & Scala - Clojure is quite unique here in combining runtime validation, generative testing, and data definition in such a cohesive way. The ability to compose specs and use them across different contexts (validation, generation, documentation) is particularly powerful.

Another impressive thing is that you can easily share the logic between different runtimes - same specs can used in both - JVM and Javascript, which surprisingly difficult to achieve even when writing in Node with TS/JS - you cannot easily share the same validation logic between backend and the browser, even for the same javascript runtime, using its native language. Clojure lets you do that with ease.

For everything, there's a trade-off. Some just accept those trade-offs, build their vision, and launch it into the world; Some waste time, lamenting that reality doesn't align with their ideals.