Taiji

I agree with that. For example, if there are challenges that require a lot of HP or strength, and others that require resistance or intelligence, both for checks and just in general. And if, let's say, a character is unlucky and doesn't "match" the required specialty, they won't have any chance. If we were doing them as a group, that would be understandable, but otherwise, I don't even know.

I think that challenges could have a variety of different solutions.

Yes, that would be almost the most ideal option.