At '09, Nadal didn't have the physical strength to compete with Alcaraz. Witness all the pre-'12 Federer-Nadal battles, Federer would hit and Nadal would chase. After Federer hit a few shots, would lose focus and the point.
The same thing almost happened in '12 AO, that's why Djokovic lost the 4th set and the TB. To play with a jackrabbit that used to be Nadal, you have to be patient, and not shoot for winners, but for him to chase.
After '12 AO, Nadal decided to add a lot of muscles, so he could go baseline to baseline with Djokovic. As the result, he lost some speed, but held on to his RG mainstay, which was his main objective. You notice that, after '11, Nadal never won AO & WB again with an active Djokovic. '22 AO was when Djokovic was expelled from down under.
I suspected that Nadal meant, at some point in his career, to add muscles and lose that extraordinary speed of his youth. Djokovic just speeded up that process.