Keeping Mbappe to stay at this time is a bad option for PSG how not, Mbappe has clearly rejected the offer of a contract extension with PSG. Therefore, if it is time for Mbappe's contract to expire at least it will be easy for other clubs or in this case Real Madrid who will easily get his signature later.
Mbappe is young and he is in hurry but moving to Real Madrid won't make him become super stars sooner. I agree La Liga is a bigger league than Ligue 1 but Mbappe can win Champions League with PSG in next few seasons but in Real Madrid, he will face with unknown future.
Galaticos 3.0 has yet been completed, just started and how it works is still unknown.
Real could definitely build a galacticos 3.0 type of situation very easily if they know what they are doing. Getting Haaland and Mbappe on the same summer will make sure that they are the best team in the world just with that, spend 200+ million on that deal if you have to and get them both. However what people are forgetting is that Pogba is finishing his contract as well, could go to Madrid for free if they offer a good amount, Dybala is ending his contract, could go to Madrid, Goretzka is on last year as well.
These are all the players who are on their last year by the way, and only Haaland needs to be bought, get a great defender as well, pay Liverpool whatever you have to, even if it is 100, and get VVD for example. Can you imagine what would happen? That team could be easily the best team I have ever seen with those additions, or at least best team next year for sure.