The Emerald Empire book gives the Imperial Families a +1 Air, but I don't think this reflects the nature that has been displayed in the stories, at least not in this version of Rokugan. Certainly if one thinks that courts mean Air and that we see them most often in courts, it is easy to imagine how one would arrive at that conclusion. However, whenever it comes to utilizing skills in an air style within the fiction-- we just see them failing and floundering over and over.
- They are really bad at manipulating people
- They can't seem to wrap their speech up in nuisance and simply imply things
- They lose every time they try outwitting or outmaneuvering people in games
- They can't perceive intruders literally inches from their face
- They seem to have little clue when it comes to stirring people's emotions positively using fashion or poetry, their attempts tend to fail
In other words, we see them trying again and again to act like an "Air" clan, only to repeatedly fail-- not just in the face of the Crane and Scorpion, but before the Unicorn and Lion as well. One might conclude that they are simply bad at everything, but there have been hints that they are quite competent at a number of things. It almost seems like a lot of the ceremony and things that are considered fine and valuable within Rokugan society weren't decided by what they excel at, but perhaps rather generation after generation of listening to Crane (and to a lesser extent Scorpion) advisors about how things should be.
- They are able to identify flaws within their own social systems, see how it doesn't line up with the tao or what would be most efficient
- They can immediately detect when others are being untruthful and quickly piece together what has happened from the evidence at hand.
- They recall all those they have encountered despite being exposed to far more people than other "clans" are
- They are good at guarding things, fighting defensively and safely transporting things
- They can organize things well, handling large amounts of reports and paperwork
- They are good at utilizing practical and grounded solutions to problems, reflected in them being more comfortable in simple brown and gray traveling clothes than the finest eye-catching robes
All of these things strike me very much as the traits of an Earth group. Like they naturally have far more in common with the Crab than they do with the Crane and Scorpion. The Crab also seem to struggle with the exact same sorts of things that the Imperials are struggling at and excel at the same sort of things too. And the Crab's clan bonus? Earth. Couldn't be further from Air.
And one could certainly imagine that in the earliest days of the empire, before all the unnecessary customs and traditions began to disrupt proceedings, having an Emperor who can see through all the distractions and deceptions to order the most practical solution to issues based on the evidence at hand would be seen as a good and wise ruler. But the more and more they allowed things to become all about appearance, swaying emotions and having a swift blade-- the more and more they found themselves simply out of their depths.
So I guess what I am suggesting is that the Imperials are actually an Earth "clan" who have been operating for generations in an environment that has become increasingly "Air" in customs and values. And while they could just force their way through via tradition and privilege, they have been forced to more and more to try to compete and aim to excel at things that are the polar opposite of their true nature. It was inevitable that they would lose their footing, screw things up and fall-- because instead of being allowed who they are naturally supposed to be and play the role in the empire they would do best, they are spending all their lives trying again and again at being something they are not.
But then-- most of this "attempting to be Air" applies only to the imperial court. I think if one met Seppun, Miya and Otomo out there in the empire who are serving as cartographers, bureaucrats, temple guards, magistrates, and so on-- I suspect they are generally quite good at their roles and I suspect they would all have higher Earth than Air.