Progression is important in an artist. If there was some kind of sheet that kept record of an artist's musical endeavours whereby boxes would be ticked if certain things had been done and left empty if not, then "Progression (e.g. lyrical, musical maturity)" is one that, in Katy Perry's case, could be left blank without any real thought having to be expended. And when considering the majority of her sophomore album, especially moments whe...