Mist of human written codebases are unusable for llm dev by that definition.

Turns out that if they're unusable by LLMs they're likely unusable by human devs. If you follow sane clean coding principles (like not having godclasses) it turns out coding agents (and humans!) can understand and navigate your codebase, especially if you use recognizable patterns, even with very light documentation.

One of these days you’ll learn about “enterprise” code

I have seen good enterprise code and bad enterprise code. Clean Code suggests progressive rewriting of bad code.

When you touch a file you have an opportunity for code clean up, add unit tests to ensure your changes break nothing, and refine the code.