They were great players at different times, to be honest I don't want to equate or compare these two players, because they were in different times. Benzema has proven that he can survive until now, and Mbappe is a young player with a bright future, but I wonder how he can survive in such tough competition. I mean he has to maintain what he has shown today, and even more he has to improve considering his young age and it is an advantage for him to accumulate a lot of experience which will make him a really great player in the future.
I think he has to brave out of PSG to improve his ability. If he stays in the Comfort zone, he will definitely not develop. He needs a league that has better competition. The level of the French league is still below the Spanish League, EPL. Actually, the decision to leave will certainly improve his ability. But I heard he will stay at PSG, so the possibility of him moving to Madrid is still just a rumour.
To improve his ability yes, he has to be brave to get out of the French 1 League. You're right because it's not very competitive at there, and PSG also have to sell him because it will benefit them, but the rumors are that Real madrid have already found a replacement for Benzema, if I'm not mistaken it's Joselu. He is a sharp and experienced striker although now at 33 years old, but his goalscoring ability is still very high. But that's also still a rumour, if Real Madrid gets him then there's a chance they can still be patient with Mbappe.
I agree that a move away from French League 1 could be beneficial for Mbappe's growth as a player. As for Real Madrid, their rumored interest in Joselu to replace Benzema seems, frankly, ill-advised. Joselu's recent stats don't paint the picture of a player capable of filling Benzema's shoes. Looking at the current state of Real Madrid's squad, I worry about their potential to perform in the upcoming season, especially if they plan to rely on replacements of Joselu's caliber. If I may express my blunt opinion, Real Madrid needs to prioritize quality over cost-efficiency in their recruitment strategies.