i have my qualms with these shot quality metrics but they're not wrong on the general point - Alcaraz has a very good backhand by tour standards, not very poor
(for newer albeit very similar numbers for the relevant players:
https://preview.redd.it/rh0qq3q0k7p...bp&s=a7d426944c12615a7c5d0b3bab0f9f3fafb14f16)
Alcaraz's (and Rublev's, for that matter) problem isn't spin - they're actually higher than many elite 2hbhs like Schwartzman, Djokovic, RBA, and Medvedev. Alcaraz's technique allows him to play aggressively off higher and/or slower balls (thus the decent results against Medvedev in bh exchanges), and he can hit very good shots down the line (even with slightly inside-out spin), but he can't consistently maintain depth and width in neutral cross-court trades and he can't defend very well with drives off that wing. imo, some additional factors are defensive footwork issues that also show up on his moving forehand, and his ambivalence about hunting forehands on hard courts, so he gives opponents more angles to hurt him in the ad court. you don't have to agree with Zoid's theses about control and technique (though they're fairly convincing), but it seems pretty clear from an eye test that something is funky about Alcaraz's backhand technique and that makes him somewhat unreliable
yeah right now his issue is that he doesn't have elite rally consistency with his forehand on the move/against depth because of his slightly inverted setup, but his shotmaking is also not fully developed in its use of angles and measured pace, so he's a jack of all trades without being enough of a master of anything (vs Djokovic or Tsitsipas), and he can spend a bit too much time donating errors
extrapolating from these comments, i tend to think that Alcaraz's forehand can lose its range on 1st returns (see Toronto & Cincinnati '23) and both his strokes can be inconsistent at getting returns in play, particularly against 2nd serves (his glaring weakness in match charting return stats). but when he's on (and it's more than often enough) he's just so clearly an ATG returner
he's Laver, Connors, and Federer fused together, actually
it's funny how people can agree with this obvious fact and not realize he hasn't peaked yet. his most dominant win at a major against a credible opponent was against Tsitsipas in RG '23 and he still lost focus in the 3rd set in the process! he beat Djokovic in a Wimbledon final while donating a set and a half lead!
would have to be very generous to say this Alcaraz was only 10% off, and he's plenty capable of ugly wins. he just couldn't rein himself back in to any sort of winning level in this Zverev match
definitely agree that his playstyle is an unbridled expression of joy and that its core is unlikely to change. i do think he can manage a bunch of improvements without changing who he is as a person and player though: more strategic discipline (dominating is fun!), resilience to dips in form, and experience dealing with the pressure of expectations