I think saying that McCallum was atrocious on defense is just as extreme as saying he's a very good defender. He was neither! He had some good moments on defense, and he had his share of bad moments as well. Many times how well or badly he played on defense was related to who he was with on the floor. So it's not a simple black and white issue. If you go to 82 games and just look up defensive ratings, you get an overall picture of how good a defender a player is, but within the confines of the team he played on. For instance, Belinelli has a better defensive rating than any of the guards that played on the Kings last season.
1. Belinelli - 101.5
2. Miller - 102.8
3. Collison - 103.1
4. Sessions - 103.3
5. Stauskas - 105.5
6. McCallum - 106.4
So your right in the sense that McCallum is overrated as a defender. His rating was the worse on the team among guards. One common denominator with the Kings players, was that their defensive rating went up when on the floor with Cousins, and it went even higher when on the floor with Cousins and Thompson. So who you play with does matter. I think Belinelli is a good example. Most people don't think of him as a defender, but on the Spurs he put up a very good defensive number. It's helps to be surrounded by good team defenders.
I'm not sure that 82 games is a reliable source anymore... nba.com is a much more rliable source, and it offers more things.
Anyway, if you go by nba.com the list (DefRtg) will go like this:
1. Collison- 104.4
2. Ben- 104.5
3. Miller- 106.6
4. Stauskas- 108.4
5. McCallum- 109.2
6. Sessions- 110.3
I didn't include Belinelli (105.1, ranked 3rd on this list) because his DefRtg was made on a team far better defensively than our team- and Defensive rating doesn't try to neutralize that so it doesn't tell you anything... but stats does show Marco is a poor defender...
Per NBA.com Players shot 2.9% better than usual on him, which is the worst mark out of any Spurs rotation player.
His Defensive rating is 105.1, which once again is the worst mark out of any Spurs rotation players- the Spurs as a team have a much better rating at 99.6.
His defensive rating is one of the reasons he has the worst net rating out of any Spurs rotation player at 0.1 (8th on the team in offensive rating).
To complete the comparison- Players shot only 0.1% better on Ben (a far better mark than Belinelli's 2.9%), on a far worse defensive team, making him 3rd best at this stat in our team after Cousins and Gay (tied with DC).
And regarding defensive rating Ben's 104.5 is slightly better than Belinelli's, better than the team in general (106.5) and ranks third on our team after Cousins and DC.
And if you like real plus-minus, Ben's DRPM ranks him 18th in the league among SG's with a positive 0.71.
While Marco is among the league worst at 92 (out of 100) with an horrible -3.12.
So the stats seems to agree with the popular belief that Belinelli is a poor defender...