I'm a Luka fan, but he does look a (hehe) little chubby these past 2 seasons and it has impacted his game noticeably. Just compare the explosiveness from his first seasons to now

Doesn't matter how you look, if you can play those kind of minutes and perform like they do you're in athletic shape. Luka and Jokic don't need to be super slim like Edwards, Morant and Westbrook because they don't rely on supernatural athleticism - they rely on other facets of their game where having a bit more mass is advantageous or at the very least not detrimental.

In any case, Doncic got bullied and embarrassed by Mavs FO's comments about his weight and work ethic(complete lies to try and save face for their terrible and shady trade) so you can look forward to a slimmer Luka next season.