Well, if you asked for a “complete mirror” then regenerating the metadata from scratch is not what you asked for. And that’s why the option to republish the metadata was hidden, because if you wanted perfect mirror then options which may undermine that could be bad.
With Mirror: Content Only or Additive, you should be able to regenerate the metadata at any time, no problem.
But I totally see how this wouldn’t be obvious from a UX perspective. There has been a lot of confusion around mirror modes in general so maybe a UX pass could be helpful? Maybe descriptions could be available on hover and options could be present in the menu but unavailable but with a description why?
(I’m not a UX person at all, I have no idea if that’s do-able with the current framework or even a good idea)