That has definitely not been my experience as of late. I have produced multiple, largeish Clojure projects with AI that have been perfectly formatted and functional. Perhaps you were using an older or possibly smaller model? I am admittedly using Claude with higher end models and mid to high effort but it has been working great for months for me at this point.

Nope, but to be fair when you're working on your own novel S-exprs you don't have LSPs to guide the coding agent. I imagine that it works a lot better in the context of a known and understood language environment like Clojure, CL, scheme, etc. The other option would be to write an LSP in a non-S-expr language to ensure that no turn can end with mismatched parens, for example.