I wouldn't really have expected that creating a directory with 600,000 directories in it would be that big a problem in 2023! This is just files! I thought we'd figured out files.
Something I have gradually learned with Computers is most types of technology really don't improve over time, they improve until they hit an "oh, good enough" point and then they just stop there, and never improve again, even if improvements are possible and someone thinks of them they won't get adopted