In the first place, you seem to be completely overlooking the fact that Pop has played everybody on the team in every conceivable combination, including starting West in Tim's DNP games. The Spurs do much more blending of their units than you acknowledge, acclimating players with players, not units. Second, you fail to acknowledge that LMA and Tim really want to occupy many of the same spots on the floor and are, hence, not particularly complementary pieces in the first unit - more like redundancies. Finally, the team would also benefit from splitting the shorter Diaw/West duo most of the time either is on the floor.
Regardless, I believe more and more that we are witnessing Tim's last season as a player. The team should do everything necessary to maximize his skill and contribution in order to win the championship with this truly historic team. We as fans should appreciate what we've got before it is gone - at this season's end, IMHO.