I agree that Lisp offers a fast feedback loop, and I have programmed in it (though not professionally) for about 14 years now.
Regarding '"interface vs implementation" nonsense', that's kind of nonsense to call it nonsense. Most of us don't (professionally) get to work in Lisp or other non-batch compiled languages. In those cases, the separation (in sane language implementations) can lead to much faster compilation time. But they also help to work with teams at scale, and make it easier to substitute implementations without having to recompile the entire thing (though you'll still usually have to relink it).
Regarding '"interface vs implementation" nonsense', that's kind of nonsense to call it nonsense. Most of us don't (professionally) get to work in Lisp or other non-batch compiled languages. In those cases, the separation (in sane language implementations) can lead to much faster compilation time. But they also help to work with teams at scale, and make it easier to substitute implementations without having to recompile the entire thing (though you'll still usually have to relink it).