Dante's expression was grim. It meant that, even though he himself could not use items procured from quantum worlds that directly affected his superpower, he was now hard-limited to the S Rank for his family and friends if they used these cores.
Why was this bad? Well, Dante himself knew his limit was not at the S Rank but at the EX. With a superpower like Quantum Entanglement and a backer like that cosmic tree, it would be a waste if he did not reach the peak of the ranking in time.
If his friends and family were stuck at the S rank, they would not only be losing out on their own power but also be limited. Anyway, that was a problem for later, and hopefully, he could find a way around it.
Right now, though, Dante was done with his rampage in the Apocalypse World. He knew that S Rank monsters posed a slight danger to him mostly due to their special abilities rather than stats, but those at the SS Rank and above likely surpassed him for now.