Smart isn't nearly as explosive as any of these three but overall, I don't think he's as far off, if at all, from these, especially at the same age. I don't think he's going to be the scorer that Rose is, or dazzle like Westbrook can but none of these three can play the defense that Smart can. Smart is as good a defensive guard prospect as has come around in a long time. He's super strong, very long, his lateral quickness is excellent, his hands are very quick and strong and he's committed to playing defense.
Take Smart and Avery Bradley. Smart's lateral quickness is as good as Bradley but he's also stronger, longer and his hands are much more lethal. Bradley can put on a good show of ball pressure but because he isn't that good of a ball thief (even though he's good for one outright theft every game), talented ballhandlers handle his pressure and often beat him off the dribble. Smart can apply the same ball pressure while intimating ballhandlers with losing the ball, which is going to make them more hesitant. When Wiggins struggled against Smart, that said less about Wiggins' handle or driving ability, since he easily drove by every other defender he faced and more about Smart's exceptional lateral quickness, hands and instincts. The same against Exum.
Smart stands a very good chance of being an all-nba defender. That's a lot of value right there. He also provides playmaking and the ability to get into the lane, with a good shooting stroke that portends improved shooting. Smart could be really good, a high impact two-way player.