It's difficult to use DRating to compare players of different positions. That becomes apparent when you take into account the type of players being guarded. Bowen would guard the premier scorers in the Leauge. Amare, not so much.
With players of the same position it becomes a little bit easier (especially PGs and PFs/Centers). While Rose and Westbrook play in different conferences, both conferences have solid players at the PG position. Also, PGs are almost always forced into guarding opposing PGs. That's not the case with many SGs, SFs and combo players. Bowen would go from guarding Jason Terry to Dirk. Same with Sefolosha.
DRating isn't so blurry when it comes to comparing two Point Guards with similar athleticism, size and playing styles.