> But it's still good for a step, no?

No. The site here is advocating a non-standard method of parsing and understanding Japanese sentences. In the long run, that will be counter-productive because the method is counter to standard grammatical parsing used by virtually every other textbook and dictionary.

The author also mixes up the standard grammatical terms for two types of adjectives, 形容詞 and 形容動詞, which suggests the author doesn't understand standard Japanese grammar very well.

I don't know why you got downvoted. If the grammar is misrepresented as you suggest, then I'm inclined to agree with you. That's unless it's not so much a misrepresentation, but rather a non-standard presentation with pedagogical benefits. It doesn't seem like you believe that's the case, though.

It's an idiosynchratic system which deviates from traditional grammar. That's a strong reason not to use it.

The author claims pedagogical benefits, but provides no hard evidence or even endorsement from educational authorities. The only endorsements appear to be from beginning learners, who by definition don't know enough to make an informed endorsement.