By that standard we have two very weak yokozuna at the moment, the percentage of Hakuho's wins by Yorikiri is even lower than Asashoryu's. And talking about Hakuho, almost 10% of his wins by hatakikomi. (Neener, neener...)
Both Asashoryu and Hakuho should be forced to retire. Kisenosato and Kotoshogiku win by right kimarite, they should replace the current Yokozuna.