Old Chinese reconstructions drive me crazy, or the fact that some scholars insist these are 99% correct instead of 'best guesses'

They are pretty well founded. You can read old rhyme dictionaries and see how the words evolved eg when borrowed by Japan at one time and then when borrowed again a couple of hundred years later. We can’t ever know 100% but it’s not idle speculation either.

Rhyme dictionaries describe Middle Chinese, not Old Chinese. Old Chinese involves much more guesswork.