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.
No way Mbape can play efficiently like the way Karim Benzema does, they both played center forward but Benzema is more suitable as a striker while Mbabe plays a good role of winger, the same position he played even in the world cup they could have been good imagination but Mbape decline Real Madrid to settle down with PSG where he is now been underrated because that dude is good with skills like speed, strength and chances converter, he is good and better than Vinicius in my opinion but that doesn't mean he can't play the role as well, Benzema was a winger to Ronaldo all through his career in Real Madrid and they switch place with Benzema when he left, Mbape might do the same but the chances os him leaving PSG will be after another season.