I'm sorry, but since we're being pedantic, this is not a proof. It's full of assumptions, some of which are wrong.

5% is clearly better than 100%

Never denied it. 0% is even better. What matters is where it's used. If it's used for FFI, that's understandable. Any other use should be scrutinized more. And that's the issue. The claim of Zig's creator is that the devs of Bun are not reliable. And to me at least, his arguments make sense.

it’s usual for Rust projects to use at least some unsafe

Doesn't seem like it. This article claims that only about 20% of Rust crates use unsafe at all. Even among those, the vast majority use it for FFI, which is kinda unavoidable.

but somehow 5% isn’t

Again, no one claimed that. But we need more than "better than 100%" when it's a JS runtime. And the "better"ness isn't necessarily linear. So, even though it might be technically "better", it might not be by much. At that point, what even is the point of the rewrite?

Again, I'm not claiming that it's actually badly written. I'm only claiming that your arguments are not adequate, and that Bun is not a reliable company, so take whatever they claim with a grain of salt.