Madonna, as the queen of pop, she had her highs and lows with sales too. There're plenty of other new female artists out there who are making so much money as well with their works, but it doesn't mean that Madonna is not the queen of pop anymore.
If someone "outsells" you once, doesn't mean you aren't what you are anymore. Ayu has her history and records that no one will be able to break or achieve in who knows how long.
Madonna is not on the top all the time, but she still the queen of pop
Just to compare both cases.