How large are these catalogs files, in megabytes? Are you trying to backup the Previews as well, this isn't necessary and would indeed be very slow.
Tree of folders problem ... don't bury your photos deep into folder hierarchies. This is an operating system limitation, there's nothing Lightroom Classic can do about it.
Also this is a user wish to the Lightroom developer team: Please simplify the catalogs!!
We're not the developer team, we're other Lightroom Classic users who can't change the software (and anyway, "Please simplify the catalogs" is a meaningless request, no one knows what you mean by "simplify")