I still think too much is made of Kap's poor defence. His one on one defence is really bad and as many alluded to earlier it's because of his lack of lateral quickness and speed. However, he is a very good team defender and he compliments that with a general high basketball IQ. Having Jermaine now start on the low blocks gives us a defensive presence that may scare some teams (obviously not perimeter ones) and it could be very beneficial to improving our overall defense.
And Jamario being considered a good defender is pretty overrated in and of itself. He's still out of position far too often and relies upons his atleticism to hide his deficiencies. It's annoying because he does have the quickness and if he ever learned to put the two together he'd be a very good defender. But last season, he had a lot of sizzle but not a lot of steak. If we could merge Kapono and Moon together that would be awesome.
That being said, offensively, it makes more sense to start Kapono right now.