Sinner lost against the best defender and likely best returner of the tour under the most unfavourable hardcourt conditions he will likely encounter over the years while having some serve trouble and slight physical problems. Barely an ace and three breaks suffered by the guy dominating the hold serve category. Charlie did play very well in the two last sets, using depth and spin on this slow and bouncy surface to make it almost impossible for Janik to hit through. Overall Alcaraz won just four points more.
@TheSlicer points to variety as a tool to beat Sinner and it is true. But who other than Alcaraz, aided by IW, can pull that off regularly? You have to be shot resistance and able to generate variety
and power. Djokovic won with hyper aggression in Turin but crashed in Melbourne, Medvedev came out playing some of his best tennis ever but was ground down. Alcaraz dominated Sinner in slow IW last year but was blasted off the fast court of Miami.
Overall this loss confirms a lot about Charlie and Janni. Both will make their tactical moves and will have an easier or harder time to execute depending on form and conditions.