I don't know or care who will win more slams.
Carlos is an outstanding young player and has already delivered more than could reasonably be expected of him at his age. He is rightly considered a phenomenal talent of our sport. There is every reason to suppose that he will continue to excel in his career, all else being equal. He seems a sweet guy, and is liked by his peers on the tour. He has a good team and continues to evolve his game, having established success on all surfaces.
Jannik is a superb talent, who is realising his potential and will most likely also achieve great things in his career, all else being equal. He seems like a pleasant chap who impresses me with his calm demeanour and increasing serenity on court when he plays, which I believe enhances his ability to deploy a strategic / incisive game. He has a really good team - I like seeing Cahill out scouting his opponent's matches.
What a prospect for the future of the sport these players are. Given their young ages, we tennis fans stand to be the beneficiaries of their respective talents for some time to come. I anticipate that they will share the spoils on tour not just between them, but also with others that are also coming up/will come up. That bodes well for the sport.
If mentioning Carlos / Jannik and slams, the former has 2 slams already and the latter none. The Wimbledon win by Carlos has been acknowledged by many pundits as one of the best Wimbledon finals ever. He played an in-form Novak who was generally unbeatable in much of 2023. The calibre of success already enjoyed by Carlos is top tier, and Jannik has yet to match it. That is simply a fact. Can Jannik match it? Given his considerable skills, yes. Will he do so-who knows? Nor is it possible to know what else Carlos will achieve.
However, I have no problem though in hazarding a guess and say that Carlos is likely to achieve greater success in GS title wins. I base this guess on an extremely scientific premise - my soft spot for the boy.