I also have the same thoughts, if there will be a player that can influence Luka to keep his body in shape, that could be no less than Lebron James who has been playing for 20 years and keep his body on top.
So just imagine if Luka would have the 10% of Lebron's mindset when it comes to their physical body, who knows, maybe he can also stay in the league for many years and could bring a championship all together.
He can for sure, as Luka idolize him and by his guidance it might be possible for Luka to change his attitude in terms of conditioning his body, as we wall knew how LeBron invest with his health to last till now, his kind of discipline giving him that huge opportunities to keep his career up to now, it's best to give that mentality and guide Luka to base on it.
Luka is still young and with the kind of capabilities, his skills and talents will continue to advanced just need to prevent getting serious injuries to keep his chase in winning a title.
Lebron did have other teammates before who played with him for years, and never really had Lebron type of discipline to fix their body. How many players that played with Lebron reached age 40 and still played? Many players ended up retiring earlier. Look at players like Wade, Bosh, Love, they all retired already and that is why I am not entirely sure if Luka Doncic would be an outlier and end up having a longevity of Lebron.
While I agree fully that Lebron takes care of his body like no other, and spends millions of dollars every single year to keep his body in shape like this, we also need to remember that he is a freak of nature as well. His body is unlike anyone else, even before all of this, even when he was in high school, this dude was freak of nature from day one.
So while he is definitely keeping his body in check and constantly takes care of it, I am sure that Doncic will do maybe a bit better, but not as good as Lebron, we won't see Luka get back in shape THAT much, maybe a little but that's it.