I think it's worth more scrutiny today, rather than less. Your claude code can barf out "a rewrite" but is it any good? So far the answer is "no" (see anthropic's C compiler, or a more recent port of bun).

Software is still the best specification for existing behavior..

I'm not following because a) The bun rewrite was a success b) the C compiler wasn't a rewrite and c) "Software is still the best specification for existing behavior" seems to imply that rewrites are achievable because we already have a working version that functions as a spec?