I disagree that debugging is a superset, it's a different skill. It's possible not to know how to design and implement an algorithm, but know how to dig into so

I disagree that debugging is a superset, it's a different skill. It's possible not to know how to design and implement an algorithm, but know how to dig into somebody else's implementation and vice versa. But being harder is not even about the skills themselves, it's about mental effort it takes to do something. And designing and implementing things is certainly much much harder, than digging into something already designed and implemented.