I agree with this completely. I read an article by a professional Go player who recommended, for the best improvement of Go skill, that 90% of your Go time should be spent doing tsumego (the other 10% playing games presumably) and that the tsumego time should be split evenly between problems that are easy, medium and hard. I mention this as it is some professional support for the idea that a broad range of difficulty is probably a good thing.
But all that is more a discussion of how puzzle solvers should approach tsumego, which is getting a little off topic. The main thing here is to decide on how the difficulty drop-down menu in the tsumego creator should look. How about this:
Elementary
Easy
Medium
Hard
Very hard
30-20 kyu
20-10 kyu
9-1 kyu
1-9 dan
30 kyu
29 kyu
28 kyu
(etc)
7 dan
8 dan
9 dan
I think this is the solution that would please most people as the options are there for individual ranks, wide rank bands or general descriptors (easy, medium, hard) as people prefer.
Can we at least agree on that?