Honestly, I think the way PEs are set up is just a necessary bit of abstraction in order to keep the complexity of calculating pleasure down to a manageable level. I mean, speaking purely in terms of physical actions, would, say, the relationship between Sebastian (a cis man) and Caramel (a transman who has not gone through sex reassignment surgery) be different from a cis male couple's relationship? No doubt it would, but then, not all cis male couples have the same preferences in terms of sexual actions either. They aren't all into anal sex, they don't always have one much more femme partner and one much more butch partner, they don't all find very muscular figures attractive, and so on.
The fact is, sexual acts and preferences in real life are far more complex and varied than either "what gender are you" or "what equipment do you have," and it can only get more complicated when you factor in the fantasy creatures that are found within Otherkind, which have options like transforming into different forms
, swallowing you whole
(holy crap I love that card, and I'm not even really into vore,) and of course, all the tentacles
. But from a game design perspective, you want it to be easy for players to understand what the result of any given move will be, and you don't want to have too many abilities in your game that do essentially the same thing, which means that trying to do anything like giving Furres a separate aptitude for every possible sex act, while it might be "realistic" in some sense, would be completely unworkable. What you need to do is to group methods of giving pleasure into a manageable number of categories, like how so many RPGs separate damage into categories like fire, lightning, and ice, or slashing, piercing, and crushing.
And since we're already classifying the Furres themselves by what gender they identify as for the purposes of deckbuilding and resource management, from a game design perspective, it's much easier to figure out how much pleasure each Furre deals to other Furres if pleasure is determined on the basis of the same categories, rather than also having to keep track of orthogonal categories for the Furres' physical attributes, which most of the time but not always correlate a certain way with their self-identified gender. And anyway, even when it comes to real life sex, regardless of what you and your lover have got between your legs, there are always enough possibilities open to you that love will find a way, as it were.
In summary, card games can't be completely realistic and still have comprehensible rules, and sometimes you just need to repeat to yourself "it's just a game, I should really just relax."