Defensive rating really slants in favor of big men and against guards, which makes Sulaimon and Winslow's grouping with Plumlee, Okafor and Jefferson in the 101-103 range pretty impressive, even if you consider the stat in a vacuum to be almost entirely worthless (I do). I think a fair use of the stat is to look at guards on one team together, bigs on one team together and wings on one team together, which of course winds up making the stat almost entirely worthless, since there are usually at most 2-3 players to compare in each group.
Kentucky by defensive rating in SEC play: Towns, WCS, Dakari, Lee, Harrison, Lyles, Harrison, Ulis, Booker. If you look at the full season, to include Poythress, it's basically a 100% correlation between size and defensive rating.
For an exception, Aaron Craft his senior year had the best defensive rating on his team, and his team was #3 on defense. I interpret that as meaning Craft's defense is the standard for a point guard. TJ McConnell was very close to beating out Aaron Gordon for #1 defensive rating on the #1 defense. I think the new stereotype for white point guards is that they play great defense but have broken shots and no range.