That's factually untrue. Google, Microsoft, Facebook, Twitter, Airbnb all have a huge monorepo. Splitting it out is obviously not necessary with the right tools.
The danger with mouthing off on HN is that this place is thick as thieves with people who actually do or did what the bloggers whinge on about.
Though in this case, the blogger has worked at all three of MS, Google, and Twitter, so I wouldn’t be quick to disregard him either.
He spent a lot of time optimizing ‘hg’, and one assumes that the Iguana did what could be done.