What the Warriors did was completely within the rules. They would be stupid not to replace their worst starter (Barnes) with the second-best player in basketball. That doesn't mean it wasn't cowardly or against the spirit of competition, though. I don't begrudge Durant for leaving OKC. I can't stand the way Westbrook plays basketball, and I couldn't imagine being his teammate. OKC also has to be among the worst cities to live in as a rich, recognizable athlete.
But he took six meetings. He very well could've gone to the Clippers, Spurs, Heat, or Celtics. Boston, in particular, offered him a chance to remain "the guy" on a team with a bright future. Instead, he took the path of the least possible resistance. It's never been so easy for any team to win a title in the modern pro sports landscape. And unless LeBron goes to Houston and has two superstars and the best role players in the league flanking him, it won't be hard for Golden State.
Say what you want about LeBron, but there were no guarantees that Miami would work out. There's even an argument to be had that it didn't. The Heat were the lesser team in three of the four Finals appearances (they should've beaten Dallas), and they lost two of them. Even if LeBron does join the Rockets, though, they still won't be better than Golden State on paper. They'll just be better in the playoffs, because that's where LeBron feasts.