i don't know many people that rate Luka higher, but his defense is nowhere near terrible. he's improved it significantly year over year and had by far his best defensive season ever in 2021.
https://www.mavsmoneyball.com/2021/1...ericks-defense
he has clear flaws there, the most glaring being he whines to refs rather than getting back on D which kills the Mavs' transition D 3-4 times a game (we call it the Boogie special), and he only gives so much effort on that end because of the offensive load he carries. but these takes of him being terrible defensively i assume come from those who think he still plays the way he did his rookie year. he led the Mavs in defensive win shares this year, easily, and was behind only Dwight Powell for DBPM.