Hierarchy of categories and urls path

Hello everybody,

First of all, if there is a better place to post this inquiry on this forum don’t get mad at me. I will understand.
Second, thank for your support.

Straight to the question:

So I’m using wordpress’ categories so I can discriminate between topics that follow a natural hierarchy. The issue presented by using this logic is:
I have “x” category
eg: Cat
and: Dogs

Some of the post involving cats are about comparison among them. The same happens with the Dogs category. I thought that using a TAG “comparison” would resolve the functionality I’m expecting which is:
If I visit Cat category (AKA: myblog.com/category/cat/) I will be able to see both Cat posts and Cat posts that compare cats.
If I visit Dog category (AKA: myblog.com/category/dog/) the result is the same as the one above.
If I visit the “comparison” tag (AKA: myblog.com/tag/comparison/) the result is both Cat and Dog posts that are talking about differences on these animals.

Since this is not just a blog about Cats and Dogs…

Then I would like to discriminate trough a url path, so I can list comparison of selected animals. Eg: myblog.com/tag/comparison/ +Dogs +Cats +Unicorns

I have tried Categories and Subcategories but it seems I wasn’t using the correct logic. Eg Category “comparison” with subcategories [Cat, Dogs, Rats, Unicorns]. I thought I could uncheck the parent category “comparison” and avoid those to be listed over there.

Any help, call it idea, correction or clarification will be really appreciated.