One year can make a big difference.
The 1999 Eagles went 5-11 with a rookie head coach in Andy Reid and a rookie quarterback in Donovan McNabb leading the way. The Eagles went 11-5 the next season, made the playoffs, and even won a postseason game. The 1999 team was tough and competitive, with several close losses. The 2000 team found a way to win those games and played much better football.
There was definitely more talent on the 2000 team, but one of the key reasons for the improvement was the year of experience that team had.