Mbappe has the chance to get on Messi's and Ronaldo's level. His speed and technique are insane. I wouldn't understand him leaving now as the teams he is dreaming of, namely Barcelona and Real Madrid, are not the same anymore as they used to be. PSG has a good future and a couple of clubs in the Premier league are highly attractive. Barcelona and Madrid are a bit outdated I think. I hardly know any of the players anymore and they don't really have any superstars. If Agüero is the best player Barcelona has to offer, my lord, it is game over for them.
Real Madrid was literally on semi-finals of UCL last season, PSG lost a way before that. I do not know which game you are watching but Madrid is still a good team, we do not know how they will be like this season but I can only speak on behalf of last season and they were really good, better than PSG for sure.
This season however PSG got every good free player in the world, and they are definitely great right now, and Donnaruma is young so he may stay there, but aside from that all those Messi, ramos, wijnaldum type of acquisitions are older players who will not be there for too long.
Mbappe could learn more from Messi that is for sure and he should stay I agree with that, but if he wants to leave, Madrid is not a terrible choice, plus when you add Mbappe to Madrid and remove Mbappe from PSG, that surely makes Madrid a better club as well. It is not just about names, you can get the best 11 in the world but if they do not get alone well, then you will not be good.