You can't procreate, that sounds like a pretty big difference in capacity?
What you mean is that they don't have sexual attraction towards people of an opposite gender, where if they had a relationship with them, that relationship would encourage procreation.
To me that just doesn't seem like a "difference in capacity".
I personally don't want children, and will probably seek out a partner who likewise does not want children. If I encounter somebody who wants lots of children, I will see that we have different life goals, and I probably won't be very keen on being in a relationship with them. Do you consider me "damaged" or of "diminished capacity" because of it?