When he got the GM job on a permanent basis, Griffin said the team, as then constituted, needed to get bigger, smarter, and tougher, plus they needed to improve their shooting. It was pretty clear from the beginning that his regime would be more focused on offense than the team was under Chris Grant, and in fact Griffin admitted as much.
James Jones and Mike Miller, not to mention Kevin Love, weren't exactly brought in for their defense. Shawn Marion was, but he isn't even in the rotation.
Defensive versatility is sought after by all NBA GMs. The mere potential to guard multiple positions will make you a lottery pick (see: Aaron Gordon, or Earl Clark, for that matter). Rumor has it that if K.J. McDaniels had been available, the Cavs would have drafted him instead of Harris. He's a guy who fits the "guards multiple positions" bill.
Perkins was simply insurance against a Mozgov injury. Under normal circumstances, no doubt Griffin knew he wouldn't actually play.
If there had been an on-the-court role available, I think a stretch big who could pair with Thompson or Mozgov would have made more sense than Perkins.
My point is that I don't think the drafting of Harris or the signing of Perkins should be viewed as an indicator that Griffin doesn't value defensive versatility. However, it's hard to find defensive versatility and good shooting in the same player, even if you are drafting higher than where the Cavs will be drafting. Compromises need to be made.
Keys hits on a key point that the 3 prime bench players can all play multiple positions. It means they can get away playing only 8 guys most nights. Also helps that the team doesn't foul much. My hope is that, having worked together for a year, Griffin provides Blatt with a roster with more than 8 guys he is willing to play in a regular season game.
I don't want to answer for him, but Keys said just upthread that the guys he likes for the Cavs are Caris LeVert, Delon Wright, and and Cameron Payne. Most mocks I have seen have LeVert going ahead of the Cavs' draft spot (23-25 range), though there is a chance he falls due to his injury. His stat line is similar to Tony Snell's in college -- both 3 year player too. They also look a bit alike. I didn't like Snell coming out of college and thought he was a bad choice, but he has admittedly been decent for Chicago.