Your analysis of the game and football is top tier, Real Madrid never planned to let Benzema leave but as he wanted, they couldn't say no to tie him down. If well considered he has impacted majorly for Real Madrid. He should hold the position of the third Real Madrid highest goal scorer after Ronaldo and Raul.
Actually, Real Madrid planned on letting Benzema go. They didn't try to persuade him, they didn't offer him a new deal. A good number of the Madrid fans wanted him gone. They say he's old, slow, and finished. They blamed him for the loss against City, they also blamed him for the league loss. They said he has declined and could no longer play for Madrid.
The mistake Madrid made was thinking getting Mbappe would be easy. They knew PSG won't want to lose Mbappe for free so they'll sell him this summer for a lower fee. They believed they would get Mbappe to replace Benzema.
At this point, Mbappe is not all Madrid needs right now. The defense is in chaos and the midfield is not creative enough. A midfield of Camavinga, Bellingham, Valverde, and Tchouameni is not a creative midfield I'm afraid. They may win games but when they meet teams that are very compact in defense they won't be able to penetrate. That's exactly what happened against Barcelona and Juventus in thepre-seasonss.
Right now the only creative players for Madrid is Vinicius. If he can be kept quiet then Madrid is toothless.