How Archaic is James Legge's Written Chinese in this Side by Side English/Chinese Book?
This is a hard question which even puzzles many advanced Chinese researchers, such as this piece of The Question of Authorship in Chuang Tzu

http://140.122.100.145/ntnuj/j29/j29-10.pdf


found here.

Put simply, it may be a little too hard for Chinese writing beginner to pick it up something like Chuang Tzu, being hard not only for the text classical grammar text, but its introduction to a world of idea.

Just because it's hard to learn doesn't mean it's not helpful. Chuang Tzu is a legendary that has been continuously influencing many people.

On the website you mentioned, that piece is quite classical formatted, though not necessarily the authentic one. It's really hard to tell how authentic a piece of writing like that can be, and that's the job of some specialists, such as historians.

Hope you learn Chinese well :D