I guess it all depends on what your looking for.
The lightness of the diamond bows are what had me intrigued in them. I've read where one of the diamond guys- Paul Pickering- commented how there bows were more geared towards bowhunting and bowhunting ranges.
If I ever shot 3-d or target I'm sure a heavier bow would be better. But for me, I like them to start at least somewhat light as they are only going to get heavier when the excessories are added to them.