I also think OD is too important in this game. It annoys me no end to see my guards shooting 35%. Takes a lot out of the game for me.
Fact is, if they can have shot blocking as a separate skill for big men then they should also have stealing separately for perimeter defenders. There are lots of players who have above average steal numbers but are not necessarily the best defenders. This would even things out a little on the defensive end.
But I think the most important reason things are unbalanced on the defensive end is that players have no trainable physical skills. Physical ability is crucial in defending - strength, jumping, quickness matter a lot when it comes to defence. But making such changes would probably require an overhaul of training, so I don't know if any of this is viable. Would love it if it happened though..