1. Raptors front court was/is struggling defensively
After getting eaten up by some elite Eastern Conference big men in the last month--Carlos Boozer (36 and 12), Brook Lopez (22 and 9), and Greg Monroe (35 and 10)--it's not hard to come to the conclusion that the Raptors front court is struggling on the defensive side of the ball, but here are some other telling stats to back this up.
a) Last season, the Raptors ranked T-9th (with Indiana) in rebounding rate, which measures the percentage of missed shots a team rebounds. This season, the team ranks 24th overall in the same category. Sure, there have been injuries affecting this stat (mostly talking about JV here), and Ed Davis being forced to play heavy minutes at C wasn't ideal, but the point is, the Raptors aren't rebounding.
NOTE: The drop in Defensive Efficiency ranking has been just as big, going from 12th overall in 2011-2012, to an abysmal 26th overall this season.
b) Before you point out that the drop in rebounding rate is only a symptom of the larger problem, and that Toronto's big men shouldn't shoulder any more blame for bad defence than the backcourt, let me point to this:
The PER numbers on the right aren't representative of the Raptors players, but their opponents. That means that the PF and C positions have been the weakest defensive positions for Toronto, giving up a PER average of just over 19. Even with JV's return, I don't imagine this will change by the end of the year.
Overall, the least productive positions on the team were actually C and SF (because offensive production at the SF was so poor), ranking 27th and 26th overall respectively. It's obvious that production from these positions will increase significantly with the addition of Gay and the return of Valanciunas, but when you're talking about defence, there's no denying that the Raptors frontcourt has not been very effective. Rudy is a good rebounder from the SF position, but as he's going to see some minutes at the PF in Toronto, it'll be interesting to see if he can hold his own defensively.
2) The best pre-Rudy 5 man floor unit: Calderon, DeRozan, Anderson, Johnson, Davis--highest points per possession [1.3] and lowest points per possession allowed [0.99]
These were 5 of the top 7 (healthy) Raptors players, so perhaps this unit being the most efficient doesn't come as a shock. The interesting part is that both Fields and Pietrus saw more minutes with this unit than Anderson, whose simple rating (similar to PER) has him as the 2nd most efficient Raptors player of the season--Amir ranking #1.
The Rudy Gay trade has me putting my large collection of "Free Alan Anderson" T-shirts into storage, but this isn't necessarily a bad thing. Anderson may not play 30+ minutes anymore (he was averaging well over 30 in the 5 games before the Gay trade), but he's still a fearless scorer that is perfect for Toronto's bench unit.
It's hard to predict what Toronto's front court will look like after the trade deadline, but I imagine the 1-3 starting spots of Lowry, DeRozan, and Gay are locked in for the season, and will be able to maintain a high efficiency regardless of who starts at the 4-5. Hell, even Aaron Gray's looked decent in four consecutive starts at C.
Best unit going forward: Lowry, DeRozan, Gay, Johnson, Valanciunas.
3) The Raptors were/are taking too many jumpers
There's no question that Calderon was a big offender here, but Lowry is also to blame. He often devolves into a jump shooter instead of using his athleticism and explosive quickness to push the ball up the court or get to the rim.
DeRozan's never had a fantastic first step, and even though his mid-range game has been more effective this year, he still settles for a lot of long, contested two pointers: the worst shot in basketball. Another player who's guilty of the same is Amir, who will gladly take the available 18 footer, even though he's clearly better served playing around the rim.
While I don't think there's anything universally wrong with having players take long shots, there's something wrong with having most (if not all) of your top players doing it.
Above, you'll see that 73% of Raptors shots are jump shots, whereas their opponents only settle for a jumper 64% of the time. The eFG% numbers actually show that Toronto shoots their jumpers more effectively than their opponents, but because they take so many, they end up being less effective overall.
The addition of Gay doesn't do much to help this situation, as he, like Lowry, tends to get a little too comfortable taking long, often contested jump shots. Unfortunately, when Bargnani gets back, I imagine this will be an even larger problem. This is one of the many reasons why I would encourage Bryan Colangelo to move either Bargnani or DeRozan before the trade deadline and get rid of some of the skill-set redundancies on the team.