Many of these sub-categories have useful filters that aren't available in the general product list, but if I want to use them, I must open tabs for each category.
If this site could do a union on all the categories, offering sub-filters where available, filtering in the products that meet those filters and categories, out the products that have different categories, and in the products that have no categorization at all for that filter, that would be very useful.
On the other hand, if Amazon would just do a better job of curating the metadata on all these products, that would be great too. Maybe it takes a full time effort for a few people to maintain the compatibility lists for all the phone cases on Amazon. But that has to be more efficient than having thousands of under-informed consumers try to repeat that work over and over again...