Ron Artest at his best was a defensive maniac. I was watching the NBA in the mid 2000s. I wouldn't argue that he wasn't better than both Bowen and Kirilenko when all three were at their very best defensively. But for me personally, I don't think Artest was so much more significantly better to put him in his own category.
Each at their best, Artest was probably the best of the three. Exceptional lateral quickness, strength, and quick hands. Very freakish (his lateral quickness especially) considering how much weight he walked around with. Bowen stuck on players like glue, would get in their shorts, tug, pull, clutch, grab, and push the limits of the defensive rules to gain every advantage. As I mentioned earlier Kirilenko probably used his length and quickness combination better than anyone I've personally watched play (I didn't watch Bill Russell or Wilt).
So yeah, I wouldn't argue if you said Artest was the best. But I don't think he was on a completely different level. Different styles as perimeter man defenders. But all around the same caliber. That's my opinion.