The back door cuts for open layups are due to Harden's lack of focus. The perimeter one-one-one matador, turn-style is due to poor fundamentals and yes, laziness. The poor switching and half-hearted defensive rotations are due to both a lack mental focus and laziness. All in all, I believe he will mature over time and become more disciplined in the years to come. But not without a head coach--like Pop or Thibs--who demands it consistently. The regular season is a grind and young, high usage players often lose interest on the defensive side. Expect a more aggressive and disciplined Harden on both ends this postseason.
All of those guys are better offensively than Harden. Dirk was at least an average defender in his prime too. Moot point. Look at how many more wins the Suns got when Nash came. Not comparable.