While your conclusion is correction, your logic is flawed. There is nothing about the other partner’s “procreative (=reproductive) potential” that makes the sex act legitimate within marriage. You could have a couple where both the husband and the wife were infertile for any reason, and sex between them could still be considered “procreative” though not reproductive.
The act of sex, absent of any means against conception, is inherently procreative because God created it to be in favor of creation. Our priest explained that being procreative is not just limited to reproduction but also being fruitful in other ways. The unitive aspect of sex within marriage brings about this fruitfulness, thus fulfilling the procreative aspect as long as no means has been used to frustrate it.
Homo"sex"ual “sex” can never, ever be procreative, nor can it be unitive in the sacramental sense though these poor individuals may very well experience a closeness because of their actions.