and BTW, "Britney" is not a perfect era.
It lacked in the singles department

. . . and the album wasn't the best to be honest.
her most perfect eras are "In the zone" and "Oops I did it again". those eras stood out in everything, the material was strong, the singles were major successes, the critical reception of the albums were good, lot of promo everywhere, great music videos, etc.