For the purposes of this argument, I will define mediocrity as winning between 35 and 45 games and not advancing past the second round of the playoffs.
There is an oft repeated theory that if a team finds itself in the realm of mediocrity at any point in time that it is doomed to stay in that realm for perpetuity. This claim is a myth.
Some recent examples that prove the above to be a myth:
The 2009 and 2010 Lakers:
Before winning the title in consecutive seasons, they were solidly mediocre during both the 2006 and 20007 seasons, winning 45 and 42 games, respectively and getting knocked out in the first round during both of those seasons. In '08 they won 57 games, made the finals, and--woo too--lost to the Celtics. Unfortunately, they won the next two.
The 2011 to present Miami Heat:
After winning the title in 2006, the Heat quickly returned to mediocrity. In '07, they won 44 games and lost in the first round. They were truly bad, the following year, but got the non-contributing Michael Beasley as their consolation Prize. In '09 it was back to mediocrity, 43 wins and a first round loss. In 2010, they barely escaped my criteria for "mediocrity" by winning a whooping 47 games, but they lost in the first round of the playoffs again.
The 2004 Pistons:
In 2000, they won 42 games and lost in the first round of the playoffs. The following year, they dipped to slightly below mediocrity, winning 32 games and missing the playoffs. This was followed by two consecutive 50 win seasons where they made the semifinals and then the finals in the East. The following year, they won it all.
The 2008 Celtics:
Between 2000 and 2005, the Celtics were mediocre for all but the '02 season where they managed 49 regular season wins and a trip to the Eastern Conference finals. In '06, they dipped to just below mediocre, winning 33 games and missing the playoffs. I doubt there's any need for reminders about how '07 or '08 ended up.
The facts should put to bed the argument that any amount of time spent as a mediocre team inevitably can only lead to perpetual mediocrity. There's no truth to that myth. As a matter of fact, as shown above, it's not uncommon for teams to go from mediocre to champions in a very short amount of time.