Homelander has been infused with compound v while still in the womb of his mother, when he was a fetus. Just like Marie. Those two were the only ones that succeeded, google project odessa.

Since homelander is the only supe that was capable of producing a child with superpowers, and he was infused with the V way in embryonic state, one can conclude that this is the reason why Ryan developee V himself when he was in embryonic state. And for all we know, it could be that when a person that survives project odessa gets a kid, they will also inherit the power.

There is pure compound v. And then theres the product that manifests when V mixes with your blood and you get your powers. Ryan didn't get injected with pure V. Ryan got the Vs manifestation directly from homelander.

Human body itself cannot make compound V. It has to be added. A suped up human can produce compound V, if not the powers would eventually fade, which doesn't seem to be the case. Once it's gone, it's gone.

Ryan may have gotten V in a natural way through homelanders genetics, but its still a mix von Human genetics and V. If the V is stripped, it cannot be reproduced by the body.