I think you are in a bit too deep. Self-creating scorers who play bad defense are the lowest lifeforms in the "basketball by analytics" world where most NBA teams and nerd fans live in.
However two years ago in the series vs Suns where Mavs lost the first 2 games Luka got heavy criticism for his lack of effort on defense being a big reason why they were trailing 0-2, and he stepped it up tremendously. If you go look at the last 5 games of that series (Mavs won those 4-1) you will see a very different Luka from what we see on an average regular season game. And it also showed up in the box: he got 14 steals in those 5 games and was really playing active on defense. He also sealed that series with stellar game 6 and 7 performances.
He can use his size and instincts on both ends, but he just coasts on defense a lot in the regular season just like Murray does. I think he isnt a top 3 player, but he is at least borderline top 5.