Beyoncé has been selling more albums than Britney since 2003, 2001 if you count Survivor outselling Britney. And that's on a WW basis. Britney owned 2000-2001 but that's not enough to claim a whole decade when Beyoncé has 2003-2009.
7 years out of the decade > 2 years
P!nk and Beyonce have outlasted/outsold Britney in every way imaginable but it doesn't matter. Britney is untouchable. Britney is Queen of the universe forever.