I don't get the comparison?
I've noticed that when trying to make comparisons to Smart, people tend to just single out players who had similar body types with no real consideration to the type of player they were.
Deron was an elite passer and ball handler early in his career, as well as being a near 20 PPG scorer. Marcus Smart is neither of those three things.
It's kinda like the recent Baron Davis comparison. Sure both were around 6'3" and both were built like an ox, but Baron Davis had a completely different game to Smart - much more based on athleticism, much better ball handling / passing ability, significantly better scorer. More of a natural PG who could also score.
Honestly, Derek Fisher would probably be a much closer comparison than Deron, although Fisher was only 6'1" he had the strong, physical body and a very similar skill set (top notch defender, volume three point shooter, huge in the clutch, more combo-guard than pure PG, etc).
I'm hoping it would be more of a "rich man's Derek Fisher" though, because Fisher was really never close to the All-Star level that many people here hope Smart will one day reach. He was, however, a starter (and very important piece) on a number of championship contenders and possibly one of the most clutch shooters of the era.