> The killer feature used to be the REPL.

The killer (hah!) feature is arguably its homoiconicity, allowing to modify the language easily within itself ("macros"). This has the obvious advantage that you can add missing features (usually) easily yourself; and exactly that causes headaches for those tasked with maintaining other people's code.

> Nowadays with LLMs writing all the code

Oh, you came all the way from the future and that's what you bring us?