Interesting question, Broken. I'll stay on Nadal also, as I know his game best. It may seem obvious, not hidden, to say his mental toughness, but what I think was under appreciated about it, at least for non-fans, was how much it wore down the opponent. The non-fan tended to attribute that to the physicality of Rafa's game, especially in the first 2/3rds of his career. Yes, he could run them around, and the sheer weight of shot broke them down. But in the really long, tough battles, the relentlessness of him wore them out mentally, too. An example I would give is the 2013 SF at RG v. Djokovic. By then, Djokovic was fully fit, and a mighty opponent. Huge battle, but in his last service game, Djokovic seemed spent. IMO, that wasn't physical as much as mental. Similarly. in the 2022 AO final, Medvedev as still fighting in the 5th. He wasn't giving over easily. But eventually, even though Rafa was 35 years old, and 10 years older, he wore Meddie down mentally, I think. He couldn't match the intensity of will in the end.
Maybe a superpower of Alcaraz's is similar, yet different. He plays most often with joy. I've never seen a player who can smile so much during a match, even when he loses a point...if it was fun, it makes him smile. I think players must find this somewhat disconcerting. Certainly, there are many things about his game to disrupt and discourage most players. But to know that you're working your ass off, and to see him to be seeming to enjoy himself so much has to be a bit discouraging. He definitely has his grumpier days, and he tends to rein himself in a bit more when he plays his most lethal opponents, at the business end of the tournament. But I think his lightness during a match is a kind of superpower.