Lebron is a much more complete offensive player and on the defensive end there is no comparison. Lebron is the best player in the NBA so I have no problem with him winning the MVP.
There's definitely a comparison defensively. In fact, statistically Durant was a better defender this year:
* Durant held opponents overall to fewer points per possession
* Durant held opponents to a lower FG%
* Durant held opponents to a lower 3PT%
* Durant was better on isolation plays, post-ups, and spot-ups
So, Durant's defense was, at minimum, every bit as good as Lebron's, and based upon evidence, was actually better.