In this video it is said that "な-adjectives come from Chinese and tend to be written in all kanji or sometimes in hiragana because the original kanji is too complicated." But い-adjectives are written in kanji too, aren't they? (e.g. 楽しい)So, in terms of writing, is there really a principal difference?
Is it true that all な-adjectives come from Chinese? It's rather surprising because some な-adjectives express such common concepts (e.g.元気、賑やか、静か、etc.)...