There is no reality where Russell is a better passer or defender than Mudiay NONE
Mudiay is more of guy who can get the ball to the right guy because he knows how the floor is spaced, ala LeBron James.
Russell is more of a thread-the-needle type passer who gets the ball through tight spots and generates buckets where it seems unlikely ala Rondo/Kidd
As passers it's unfair to compare the two, objectively speaking. As defenders, no one should care because PG defense is overrated.
Main thing about Mudiay is that he'll probably end up a John Wall type player that can stuff stat sheets and makes mature decisions with the ball, and the ball will probably always be in his hands so he'll always be able to make good passes happen.
Russell will need to step up as a scorer on and off the ball in order for his playstyle to work because his passing style is based on his threat to score.