True, but you still cant do first paint until all css is loaded, and for people with fast connections, the latency of the extra roundtrip matters more than the size of the file downloaded (within reason)

An alternative would be keeping theme state in JS as suggested at the end of the article which improves the cache-ability of the css file as themes change.

Yeah you'd have to load it in async to avoid that. You could start with a gray base and have the theme color pop in. Flash of original color.