The Marcus Smart to DWade comparison is fair as long as they also compare Avery Bradley to Kobe Bryant and James Young to Kevin Durant.
I think you're missing the point.
The Comparison of Smart to Wade isn't suggesting he's on the same level - it's a comparison of player type and skill set.
Avery Bradley is a '3 & D' player who has a defense-first mentality. He's an undersized SG who isn't very strong, has a mediocre handle, medicore passing and an offensive game limited to open threes, pull up mid range jumpers and baseline cuts.
Kobe Bryant in his prime was an offense-first player who also had excellent defensive skills. He had the size and strength to play either SG or SF, and was always an elite ball handler and passer for his position. He has always had the ability to score in every way, from jumpers to drives to post game. He is not even remotely close to AB in terms of player type.
James Young is a SG with legit SG size and a solid jumper, slightly above average athleticism, pretty average passing and rebounding...and that's about it (so far). Durant is a SF with the height and length of a PF, the athleticism of a shooting guard, elite offensive game, and exceptional rebounding and passing skills.
Again, these two guys have just about nothing in common except they are both skilled perimeter shooters.
Comparing Smart to Wade however, there are a lot of similarities. Yes Wade is (and always was) a far more accomplished scorer than Smart is right now. But ignore that one aspect, and in every other part of their game they are extremely similar. Both about the same height and weight, similar strength, length and athleticism (Wade slightly more athletic). Like Smart, Wade predominantly played PG as a rookie and averaged around 5-6 assists and around 5-6 rebounds (which I suspect Smart will be averaging once this season is over). Like Smart, Wade was an absolute defensive beast in his prime - I would say he was one of the top 3-5 perimeter defenders in the league.
I seriously doubt that Smart will ever be on Wade's level offensively - Wade has been one of the league's most dominant scorers for the past decade. I do think he has the potential to be a very productive (16-19 PPG) scorer though 3-4 years from now. My instincts tell me that 3 years from now Smart will be up around 16.5 points, 6.5 assists, 5 rebounds and 1.7 steals...and they are very nice numbers if that comes true.
Aside from Wade I thin the next best comparison is probably Tyreke Evans, though Smart is already a much better defensive player and probably already a better shooter.