Derrick White is an NBA statistical enigma. On the Celtics for the regular season, he had the 3rd best DRtg (108.0) behind Vucevic (102.3) and Queta (105.6). This is among regulars with light minutes/games players filtered out. But Vucevic is viewed as a horrible defender, Queta as very good, and White as top 5 in the NBA. So I guess you can't rely on this advanced stat.
I think White gets attention for his defense first and foremost because he is a very good defensive player but also because of the blocks. He leads all guards (from what I can tell) in blocks. Blocks are fun. Blocks get attention, even more so than steals. Judging defense player by player is so subjective.
As to trading White, I would not hesitate to trade him for a good deal. There is a topic on Derrick White trades and I did not see even one that was realistic and that I would do. I want the Celtics to contend for the next 2-3 seasons, I don't want to trade White for draft picks or prospects, at least not in that time frame.