I don't understand, you've just linked to his BR page which shows some very depressing numbers? And I know I've read comments about his team defense being a problem.
Personally, I think he's an undersized poor man's PJ Tucker. It would be nice to have him on a cheap contract but I see him as the 3rd man off the bench, not the first.
I haven't heard anything negative about his team defense. I linked his BR page so you could compare his stats for yourself, they're equal the numbers he last put up in Boston which to me says he's doing as well outside of Stevens system than he was in it. The only stat that has taken a hit is his shooting percentage, which isn't that big of a concern for me. I think that happened because of the system he played in Detroit, which was primarily focused on getting Drummond the ball. He was a good defender in Boston and he started off the year strong in Detroit before they fell apart.