Alright, let's break it down. (Using a male viewer/player as the perspective.)
Male x Female porn is 50% gay, because you're watching a dude
Futa x Female porn is 25% gay, because you're watching two women but one has a dick.
Futa x Futa porn is 35% gay, for obvious reasons. Still no masculine bodies, but two dicks. Usually involves a vagina somewhere.
Male x Futa is 75% gay, because while there are two dicks and a masculine body, there's at least a vagina involved.
Futa x Male is 85% gay, because while there's a feminine body involved, it's still a dude getting ass blasted.
Male x Male and Female x Female are 100% gay. Duh.