There are some things one can get out of these "messing around" videos in practice. I remember seeing Perk in training camp in his second year playing Pierce one and one and I was surprised at how well he moved his feet and guarded the talented SF.
Pierce got his shot off at will, but Perk was on his shooting hand and in decent position most of the time. Perkins also showed more handle with the ball than I thought he had. Very surprising.
This Melo video tells me that he plays "too high." He's got to lower his center of gravity a bit both on offense and defense. I'm guessing he doesn't have enough core strength yet.