One could actually make the argument that DeRozan is the worst starting SG in the NBA (also worse than some backups). Let me have a go at it:
Atlanta - Kyle Korver: Elite three point shooter, who also rebounds and passes the ball better than DeRozan. Does not need the ball to operate and can be a huge plus on any team.
Boston - Avery Bradley: Lockdown defender, can also hit the 3 given a chance and run a little bit of point guard. DeRozan is marginally better offensively, but the gap between he and Bradley is so wide on defense that it's clear Avery is the better player.
Brooklyn - Joe Johnson: Should be self explanatory, but JJ can do everything DeRozan does except better, AND more. Knocks down the 3 at a high clip, can run your offense for you, plays superb defense and you can give him the ball, stand back and let him do his thing in crunch time. The Nets' backup, Jason Terry is also better than DeMar, pretty clear since he's an elite shooter, can be a playmaker and was the #2 guy for a championship team.
Charlotte - Gerald Henderson: He and DeRozan are basically the same player, except Henderson can actually hit threes, and plays great defense. Ben Gordon is also better when healthy.
Chicago - Jimmy Butler: Locked down LeBron during the playoffs last year, shoots the 3 at an elite level. Gives you everything you want from your starting 2, better than DD.
Cleveland - Dion Waiters: Was inefficient like DeRozan last year, but he can score from anywhere on the floor and has elite handles. Also one of the few 'Cuse guys that can actually play some man to man D at the NBA level.
Dallas - Monta Ellis: Monta is a far superior and much more versatile scorer than DeMar. He's also great at setting up his teammates and changes the game by getting into passing lanes for steals. Vince Carter, even this late in his career, is also still clearly a better player than DeRozan. Way more efficient, basically unlimited range on his 3 still as well.
Denver - Randy Foye: One of the league's premier three point shooters, who also happens to be a solid passer and defender as well.
Detroit - Rodney Stuckey: Not sure if he's actually going to be the starter, but I explained why he's better in this thread I think (maybe it was another one). I'd also prefer KCP going forwards because he can defend and hit the three and has great potential.
Golden State - Klay Thompson: Pretty cut and dry here. Scores at about the same rate as DD, but does it more efficiently and in a more useful way for his team (ie. off the ball, raining down 3s). Also a better defender than DeRozan.
Houston - James Harden: Self-explanatory.
Indiana - Paul George: Self-explanatory.
L.A. Clippers - JJ Redick: Similar to Klay, scores as much as DD but more usefully and efficiently. One of the premiere shooters in the league, also a far superior passer to DD, and his defense has become solid while DD is essentially an orange pylon on that end of the floor.
L.A. Lakers - Kobe: Self-explanatory, DD's idol, to whom he will never live up to 1% of.
Memphis - Tony Allen: Has eaten DeRozan's lunch on several occassions throughout his career (DD averaged 11.5ppg on 32% shooting against him last year). Arguably the best perimeter defender in the league. DD's slightly better offense (mostly just due to high usage, he and TA are about on par skillwise) can't make up the huge gap between them on defense.
Miami - Dwyane Wade: Self-explanatory
Milwaukee - OJ Mayo: Very similar to the descriptions for Klay and Redick. Another guy that scores like DD, but actually makes threes and has some ability to defend and make plays for others as well.
Minnesota - Kevin Martin: Scores more than DD per 36 on 60.8% TS. Can also get to the line like DeMar. I'd take KMart over him any day.
New Orleans - Eric Gordon: Should be self-explanatory, but in case anyone needs the explanation, this guy is an elite scorer when healthy, who can also run your offense and play superb defense. Tyreke (if you consider him a 2) is also better.
New York - JR Smith: Basically a version of DeMar who can actually handle the ball and shoot threes, and play D when motivated.
Oklahoma City - Thabo Sefolosha: Amazing defender who can hit the three and rebounds well. Better than DeRozan at everything except for chucking up long 2s. I'd expect Lamb to emerge as a superior 2 also this year.
Orlando - Aaron Afflalo: See explanations for Redick, Klay and Mayo. Oladipo will be better also.
Philadelphia - Evan Turner: Inefficient like DeRozan, but at least he gives you elite rebounding and passing for his position. He's also a great defensive player.
Phoenix - Eric Bledsoe: Not sure if he's actually going to start at 2, but his versatility, defense, ability to shoot the three, playmaking skill and far superior athletic ability should make it pretty clear who's better.
Portland - Wesley Matthews: See Redick, Klay, OJ, Afflalo
Sacramento - Ben McLemore: Obviously we haven't seen him play yet, but considering how sweet his stroke is, and how agile he is. He should emerge as one of the premiere 3+D guys in the league while also being vastly superior to DD athletically as well.
San Antonio - Danny Green: Watch the 2013 Finals, then try and tell me DD is better. Ginobili is out of DD's league also.
Utah - Gordon Hayward: We've discussed this already, but Hayward can score just as much as DD, while doing it more efficiently, playing defense, knocking down threes, rebounding, making plays for his teammates and with the ability to play 2, 3 or even 4 in some small ball lineups.
Washington - Bradley Beal: Should be evident from his matchups with DD where he totally schooled him, but this guy is already better than DeMar and he's only played one season. He's a better athlete, better defender, better shooter, better ballhandler, the list goes on.