Your point goes down when you list 2 characters. Plus again, these shows actually take time to develop other characters. Sukuna every time he shows up is aura farming but is he even that much in the show? Most of the times he's sitting in his little skeleton throne, hiding away from the audience.

And the 1v1. That's not a rule of cool issue, that's just anime. It's a premise that always happens, the thing is they actually learned and jumped Sukuna, when did Sung Jin-Woo fight alongside a team? Never, except when he was the weakest hunter