Who said Stripped didn't sell more than ITZ? We're just giving reasons on why it happened. Btw, that was Aguilera's second album (against Britney's 4th), released more than one year before ITZ, a year with something like 20% more albums sold, and YES, with WAY MORE PROMO.
Plus, I guess the topic is asking who will come back on top. Who has all 4 studio albums debuting at #1? Who sold 1.3 million, 610k and 750k in her first weeks? That certainly wasn't Aguilera, she barely sold 300k once.