What do y'all think about my theory regarding Uma reproduction?

Ok so ik already that Umas can make babies with normal humans or that sometimes the baby between 2 humans will be a uma (for some reason). But today i came up with a thought: what if the Umas based on malenhorses (Example: Goldship) have a futa horse cock while umas based on female horses (Example: Haru Urara) are the only ones to have vaginas? I feel like it makes sense because if Umas reproduced only with humans, the uma genes will get lost a certain number of generations in. Since we know that Umas have existed since ancient times but are still around in the modern era, i think that in the past female Umas only reproduced with futa Umas which helped the uma genes to survive until the present; this also implies that Uma×Human is something relatively recent. (Then again Umas CAN have 2 biological human parents so maybe this fact is the actual reason why the uma genetics carried over to this day.) Either way, let me know what y'all think

P.S: sorry for having used Haru Urara as an example but she was the only one i could think of wo was based on a female irl horse TvT