No, Davis' defense is not "average to average +", it is exceptional. Davis is a tremendous on-ball perimeter defender, very disruptive. And he has shown he can dribble penetrate against almost any defender.
I DO agree he needs to understand that he cannot get shots off deep in the lane at the rim with the big trees around him.
But you are vastly under-rating his overall game and value when you label his defense as merely average to average+. And by labelling him as a "scrappy" player - he is much more than merely scrappy. In football, Dremel can be categorized as "scrappy." Scrappy implies hard-working but under-talented and less athletic ... using their "scrappiness" or hard work to offset a lack of athleticism and skills. Davis is none of those. He is extremely quick, extremely athletic (a great vertical leap), with great defensive anticipation and instincts (also known as "skills") ... and hard-working) ... offensively, he has a very good dribble handle, and a quick first step. He DOES still need work on his shot selection and choices. We do not yet know whether his jump shot has improved, or his FT shooting (either or both of which would be very helpful, of course - in particular his FT shooting ... if his FT shooting becomes reliably in the 75% range, he can earn playing time near the end of games).