No. Not at all. "As designed" a hetero couple can conceive, things just aren't working as they are suppose to.
"As designed" the gay/lesbian couple could NEVER conceive.
You cannot separate "as designed" and "supposed to" when all you actually know is the state of infertiillty. Even at a religious angle, to imply they are different is to claim the intent of the designer. If the designer is the genetic code, then the body is, in fact, acting as designed and being infertile as it is "supposed to" at a genetic level. To fix that is what the insurance does even with very, very unnatural levels like invetro.
If that type of infertility is covered, then I can see the argument that the other should be as well.
If the answer to the one that cannot conceive due to a partner's lack of functioning sperm is, "lady, find you a guy with some good sperm" (which is what you are suggesting they tell the lesbians) - then that must also be the answer to the infertile couple where the husband has failing sperm. And is that really the answer you plan to give him?
Seriously, you can make the argument that infertility should not be covered, but you cannot claim "design" vs "working correct" vs "mind control" vs "get another partner" when it comes to infertility and medical insurance.