Earlier quoted context omitted.
I don't really get the Bun thing. Bun is running Claude Code which is probably the single most actively used development app there is. You say this was a bad use of LLMs, but it's been in production for a while and I haven't heard of any evidence that Claude Code has increased a significantly larger quantity of errors, segfaults, etc, than before.
I have yet to hear any evidence that the Rust rewrite was harmful. I have no emotional investment in Bun (which I'd never heard of before the rewrite), or Zig (which I also didn't know about), or Rust (which I think is neat and that's about it), so I'm about as unbiased as you can get and from what I saw the conversion was done well, and I haven't heard of massive bugs resulting from the rewrite.
The problem is what comes next. They now have code that they don't understand, and they are likely to work on it with AI in the future, but the new features they may introduce later will not have the luxury of hand-written tests and a reference code. So, unless they undertake the massive effort needed to fully understand the Rust code and deal with all these "unsafe", quality is very likely to go down, Microslop style.