Parity is the key to success for any sports league. Look at the NFL and NHL. Anybody who makes the playoffs can win it all. How does that ruin things??
The only way there can be parity in the NBA is to shorten the playoff series. Make the playoffs like the NFL or NCAA tournament, or shorten the series to 3 games. IMO, it's easier to pull off upsets in the NFL, NHL, MLB because of the lack of possessions.
In basketball, each team has about 80 possessions in a game. It's too hard for inferior teams to overcome that, especially in a 7 game series. That's why you see the same teams win every year.