I think Messi is very worried about the fact that he is far behind Ronaldo and he would like to be closer on goals scored (or maybe he's trying to get away from Levandowski even further). Therefore, he uses every opportunity to improve his personal statistics. It may be selfish, but such motives are understandable.
I think mbappe should stay a little more, he will gain more from Messi than any player. They make a perfect duo already. Their last 2 matches was either one assisted and the other scores and vice versa. The Messi and Mbappe dynamic reminds me of the Ronaldinho and Messi dynamic in 2004. Obviously not as legendary but still similar in some ways
I think one season is enough to gain experience from Messi and Neymar. Mbappe is already an accomplished player, he has already played with all (against all) star players in the world, now he needs to farm statistics and achievements to go down in history (competitors like Haaland are not asleep) and it will be more convenient to do this in Real than in PSG (which is season as if it was in the wrong league and plays with midgets and not serious rivals).