I don't think Winston was ever best RT in the NFL. He may have been best RT available in FA the yr the Chiefs signed him. They probably overpaid for him and now can't afford what he's making. Or maybe he's just not very good. Or it could be your theory that he is all banged up? Who knows.
Cheifs may draft the top LT and have him play RT for a yr or so? Or maybe they are drafting whoever they feel is the top Dlineman?