According to the defensive ratings last season everyone was poor most of the time. Just like many stats with Buddy discussions, 5 man advanced is the way to go. The best defensive rating unit with at least 10 games and 20 minutes has Fox in it. The 2nd best had Fox in it. The 3rd best had Fox in it and so on. The truth is Fox has to be careful the way he does play defense. If he picks up quick fouls then it probably doesn't matter what kind of defense the Kings play and that's just the truth. We have to see the Kings in a more aggressive defense that fits the abilities of these players before judging. We KNOW Rex's help system was garbage for just about everyone.
Look at the defensive ratings for the players that actually got real minutes in the month of February for craps sake:
https://www.nba.com/stats/players/advanced/?sort=DEF_RATING&dir=-1&Season=2020-21&SeasonType=Regular Season&Month=5&TeamID=1610612758&CF=MIN*GE*10
All of it, total garbage. Post all star Tyrese had a defensive rating 1 point higher than Fox's and a net rating of -6. 4.5 points lower than Fox. Is he a terrible defender? I think both he and Fox aren't incapable but if you're going by the advanced stats you can't be picky here they are apparently both "poor".