Well everyone will have his own definition for a 'Sex God', so I think is useless to discuss about it.
At this point of the game you only have one scene with her, but it doesn't mean that will be the only one, in future releases it will have more scenes between Rex and Rin.
And about
'you choose to share her and you get a scene, or you don't and you get blueballed' well, I don't see Rex taking the Rin's place with Ben, Hades or another male characters of the game. In the game, sex with male characters will continue happening, but that doesn't mean that Rin will be the only one interacting with those characters, you have another female characters too.
More female characters will be introduced in future releases and Rex will have sex with some of those upcoming characters, but you will have the option of use one of your monsters too. This isn't the kind of game where only the prota have fun.
As you can see until now, Rex already have sex with every female character of the game and the first scene of Rex fucking Cloy is already set to happen, but I need to develop that scene.
I have more than one scene in mind to add in the game and I will make a pull in Patreon to leave my patreons choose the first one, I make it like that because I like all the options and is a way to thanks my patrons for support me and help me to continue developing this game.