The Fame, TFM, and BTW were all promoted just as much if not more than the TD era. I don't believe Katy did nearly as much international promo that Gaga did.
Not really. BTW was promoted, a lot, but Teenage Dream's promo list is so long that even Duca gave up while compiling it.
Katy's sales, if you take in, TEA stuff, was impressive. Katy is clearly a singles artist, but her constantly selling of singles and her radio domination made up for that. PRISM doesn't even need to sell the same amount to be considered a successful follow-up. A diminished return is inevitable.
Those PRISM snippets were horrible though. And then ARTPOP is all Zedd and Madeon. I think they could both end up as losers in the end, with Miley ascending as the new ruler.