On the page BenjaminTeuber/GuideToBecomeStrong#toc5, Benjamin Teuber identifies three types of problems for any player:

• Problems where you find the right move almost instantly.
• Problems where you have to think for a while, but you can solve most of them.
• Problems you cannot solve completely - of course, you sometimes find the right move by intuition, but you can't calculate completely.

It would be nice if for most players, they could find problems of any of the above types by varying the page difficulty. So for dan players, this would be: Expert, Advanced, Intermediate. For strong kyu players it would be Advanced, Intermediate, Beginner. For weak kyu players it would be Intermediate, Beginner, Introductory.

Or something like that (these are rather arbitrary groupings of players).