I can't think of a single team that has not been a contender in the last 35 years - even the worst franchise in NBA's history, the Clips, have made some noise the last couple of years.
Any team in Charlotte
Also, using 35 years kind of proves the point. That's a long time. I think you'd ideally have every team be a contender or fringe contender at least once in 10 or so years (if parity is the goal).