Ryuo is just a different application of normal CoA, hence why there's such an emphasis on the flowing aspect of it.
The normal Ryuo isn't that special apart from the fact Luffy wasn't able to use it. We've seen countless characters which don't seem strong at all use this type of CoA.
The only thing advanced about Ryuo seems to be when you're able to damage your target from the inside.
So if you'd like to call "advanced" Ryuo, "advanced" Haki, I think that's fair.
But what Tashigi, Smoker, Gordon Sisters, Sentomaru, the original admirals, and Hyogoro do is not "advanced" haki or "advanced" ryuo.