Embiid is the alpha
(1) whether the others like it not
(2) whether it is right for the team or not
His playing style dominates all happenings around him. A young LeBron could challenge that but an old LeBron cannot. Jaylen isn't well rounded enough to challenge. Nor is Maxey. Embiid is the alpha with which the team revolves around.
It's hard to make him the main guy when you can't count on him to be available. LeBron is most likely not going to play a full schedule either. I think the offense starts with Maxey. However, as he'll be running point, he's not necessarily going to lead the team in scoring.
It doesn't matter how many games Embiid misses.
Once Embiid is there, he is the guy. The offense will revolve around him because of how aggressive he is and how capable he is of scoring form anywhere on the court.
LeBron isn't that player anymore. He wasn't that when Luka was available. He was less of that even when A Reaves was available. He was able to to put up numbers when he was allowed dominate the ball when both of those guys were out but he can't dominate an offense like that when his teammates are Embiid, Jaylen, Maxey. He is not effective enough anymore offensively to do that. He is too old.
Jaylen doesn't have the playmaking ability or the scoring efficiency to be the main man on a team with this much firepower.
Maxey has the scoring ability but he plays #2 to Embiid when Embiid is around.
It is Embiid. Embiid is the alpha. He won't accept anything else. He is one of the most aggressive scorers in NBA history. When he gets the ball, he will attack. He will take shots. He will draw fouls. He will score points. And he will get the ball - a lot. He has never shown a willingness to step back from scoring and become a facilitator. The guy is the All-Time career leader in points per 36min and points per 100 possessions. Folks are understating how aggressive a scorer Embiid is. He would fight prime LeBron for alpha status nevermind old man LeBron.