I got that point, just want to tell you that this is not going to work out. Globally the ways are too diverse to squeeze them in a few categories. Especially if those categories are from different kind. You can’t define on one side ways by usage and at the other side by difficulty.
If you mix different things, the chances are pretty high, that one physical way will fall into several of your categories.
I’m totally with you, if you want to split the range of highway=path into ~3 different levels of difficulty. But you need to keep the usage out of this. Each of the ~3 new categories must maintain the same usage as highway=path is currently covering.