3. Lack of Defensive Impact
D’Angelo Russell is not a strong defensive player, and advanced metrics show it. His Defensive Box Plus/Minus is a career-worst -3.1 this season, and his Defensive Rating negates a lot of the value he brings offensively.
As a reflection of that, his VORP (Value Over Replacement Player, along the same line as WAR in baseball) is 1.0 this year.
Say what you may about Stephen Curry and Klay Thompson, but Curry has generally been average defensively (somewhere in the -1.5 to +1 range in Defensive Box Plus/Minus) and Thompson earned second All-NBA Defensive Team honors last season.
Maybe Russell would have been better on the defensive end with Curry and Thompson both back healthy next year, but that would have been hard to bet on.