I feel Alcaraz is on a decline. He seems older than he should be at this age. God knows what he does in his free time.
I'm not ready to go there yet. I suppose my one concern for him is that, from what I've heard, he's pretty free-wheeling about his approach. I saw some clip from a few days ago in which he didn't know who his next opponent was. Now obviously he beat whoever it was, but still...knowing who your next opponent is and adjusting accordingly, should be part of any player's preparation. He has ungodlly talent, but at some point people start finding ways, and if he doesn't counter, he could start losing more matches.
Of course Carlos is so damn good, that he can get by--usually--on just showing up. But no matter how good you are, players will adjust to you, and if you don't make adjustments, you end up being less invincible (see "Fedal").
All that said, we cannot assume he'll have the health and/or longevity of the Big Three. He might, but he could also burn out younger. He's also more erratic than, say, Sinner. Where Jannik will have the occasional dud match, Carlos has spells of a month or two where he plays below par, so we shouldn't confuse a lull with decline - not at 23. I expect him to return to his full powers and be one of the Big Two for years to some. Lets just hope the wrist doesn't prove to be a recurrent problem.