Britney's had different peaks according to the career aspect we're talking about. For album success it would be BOMT and Oops!, for single success it would be Femme Fatale, for tour success (commercial+critical balance) it would be Britney, for overall era success (album+single+tour balance) it would be Circus, for creative career control it would be In The Zone and Blackout, and for personal prosperity it would be Britney Jean
It'll be nice if popular musicians didn't peak until their 40s like most people in other occupations but given the fickle nature of pop music and the ever increasing pressure from stans to be "relevant" that almost never ends up being the case.
