If this is true, then he really doesnt carry any value
There's no team in the NBA he'd start for, right now. And no team is going to change how their offense runs for a 2nd or 3rd string C.
That's why him getting to the right team is important. There are still quite a few teams that have their C still do some traditional things.
While not as athletic, he can do some of the same things as guys like Jokic, Steven Adams, Kaminski, D Jordan, etc. He could back those guys up, give a team a couple minutes per quarter and be able to replicate parts of those guys games.
Honestly, the single biggest thing he needs work on is defense. He won't be able to play D the way Cs did 25 years ago and just camp in the lane. He HAS to get better defending the high ball screen switches/pick and roll. Even NBA backups will feast on that if he doesn't.
And, to be fair to Luka, I think people need to remember, other than injuries/foul trouble, he won't be spending much time on the court with players like Giannis, Embiid, AD and the like. He'd be more matched up against guys like Adams, Aron Baynes, Semi Ojeleye, and the like. That minimizes the limitations some.