I think most people believe it unlikely that one million line of codes can be reviewed in one week, and the fact that tests pass does not imply good code.
I have no idea whether the new or old code is/was good, just pointing out what seems like a plausible thought process for people who object to this rewrite.
I think it is interesting, using your framing, to consider why people may or may not believe that one million lines of code could be reviewed.
I mean, until very recently, the idea that one million lines of code could be written (rather than mechanically translated) in a month was unbelievable.
It is clearly the case that times have changed since the tools have been updated. So if we challenge one assumption, why not also challenge the other?
Bun presumably will have access to Mythos, which is purportedly reviewing million line code-bases (Mozilla, etc.) and uncovering real value for the devs of those projects.
I find it hard to deny extrapolating these trends to this Bun rewrite.