In many ways, Princess Mononoke is a rehash of Nausicaa, but without the airplanes, so of course it suffers. Spirited Away manages to be great even without airplanes, a notable achievement.

I don't recall an environmental subplot in Porco Rosso (which I considered Miyazaki's best film till Spirited Away came along), and there's barely one in Kiki's Delivery Service. I don't really recall one in Laputa, Castle in the Sky either.