Katy and Madonna careers are pretty similar tbh.
Both started their massive success with a controversial song (IKAG and LAV).
Both started less popular than another female which was known for her irreverent dressing and personality (Cindy & you know who hihi) but eventually surpassed her.
Katy is on her True Blue era, playing it safe and cute just like Madonna did at the time. Next era will be her Like a Prayer