Yes, you do have a point. Most people would probably prefer to dance with someone below their level than not dance at all. And I do put a limit of once, *maybe* twice, per night for the high level dancers. It depends a bit and I have a sort disjoint perception about level, too. For some reason, the women I saw come up through classes and such to pass me seem closer to my level than the women who were always better than me. I will sometimes ask women from either group, but I think I lean towards asking the ones who passed me more often than the ones who were always above me. (Another factor in my asking decision, but anyway.)
Maybe it's different where you are, but here it seems that the advanced dancers rarely have trouble getting partners. Many times they're the ones who get asked for the next dance before they can even leave the floor because they're such popular partners that everyone wants a chance to dance with them. Sometimes the difficulty for them is getting a break. They're in such high demand that they'll have to turn down requests in order to rest or socialize a bit and talk with people. I've rarely been turned down when I ask them, probably because I ask them so infrequently that they don't want to turn me down when I do, but just being at the dances I see that they do have to turn down requests in order to get breaks.