I thought the guy was useless a few years ago and wondered why CBS kept keeping him despite all the roster turnover around Jaylen/Tatum/White over the years. I was dead wrong. He's a great role player and fringe starter too. He's not a legit starting big but that's fine, he can still fill in as needed and again, he's become a very solid bench player in a real role.
I think what Luke has gotten good at, after the training staff have worked on him for years, is just being good at his role. He's no longer trying to be what he's not. He's not a stretch big even though he came into the league shooting 3s (he took 3-4 3s his first 4 seasons in the league, including his first stint with the Cs) since his second stint with them he's basically just focused on the basics for a tall bench big - screens, dribble hand offs, rolling to the rim for dunks, rebounding, and defending the rim and blocking/altering shots. That's it.
Sometimes we get frustrated at him because of those limitations, or because he gets roasted on the perimeter when they call switches on him, and because he doesn't do "other stuff" but I think they've told him "if you just focus on this part that you can be good at, rather than being mediocre at everything, you will have a career here instead of having to learn Mandarin and playing in China". And so he's just focused on that part of the game. As long as we can accept that he can be flawed in those other areas, but good at what he is in the team for, he's a very serviceable NBA bench big.