While I'm personally not too affected by the Maya/Kara choice being a hard split in routes (even if I would prefer being able to go with both), judging by the general response it might be a good idea to give players the option (probably sooner rather than later) to properly include the girl not initially chosen in the harem, rather than just including her in occasional side scenes.
Either that, or maybe rewrite the initial project scenes to include both girls? I can't say how easy it'd be to do so, but perhaps a third option (to offer all three choices in case you're very particular and want Kara but not Maya for some reason) where some other character interjects like "sorry, can I please do this on my own" so the MC just gets to do the project with both Maya and Kara? You could still work stuff like the whole "girl gets her underwear stolen by weird street magician" scene so Kara's the one who volunteers, gets her underwear stolen and has her dick peeking out her skirt (very hot), so Maya offers hers, but that'd leave her without any, so the MC still offers his underwear and the girls (plural) see his dick?
I'm not sure the best way to go about this, especially since three possible choices/routes could definitely lead to dev/story/feature bloat... but it kinda seems that in a game where the optional content has been easier choices of "do you want to see this type of content or not" that doesn't really affect the main story, forcing a definitive split like that on players might not be the best call.