Djokovic was only one year younger last season and could only be taken out at RG by the ultimate clay GOAT. Sure, Djokovic is not his, say 26 y.o. self, but he's still a pretty damn good player, and Alcaraz is also not supposed to be his "definite" version yet, so no point in drawing that big a conclusion from a match. He's ahead of pretty much anybody in the last three decades at his age, barring Rafa, and Rafa is not the only player that went on to be an ATG.
I mean, if we think about it, Alcaraz already did beat Djokovic last season on clay. Heck, he beat both him and Rafa back to back. Did that somehow "certify" his future ATGreatness? Doubt it.