This is a more complicated question I feel. Images draw me in to look, description determines if I download.
I have a preference of story over sex, but the two are not exclusive.
I think alot of devs get this one wrong. The answer is - as you said - both. But heres the thing. It needs to be both AT THE SAME TIME.
This is key, there's no reason that you can't have plot in your sex scenes. The sex shouldn't be meaningless to the characters, because then it will be meaningless to the reader. But if it has impact, if the characters come away from a sex scene with new perspectives, and it enriches their life (or even if it leads to drama) it's more worthwhile to me.
I hate that "just a dream" shit.
And this is another issue; I do not like a lack of consequence. Having spicy dreams is fine, but it shouldn't be swept under the rug. Have the MC talk about it to someone, or have it impact a choice the MC makes later (MC, not Player)
I have actually done something like that. There's a character at the beginning of the story that the MC could have sex with pretty quickly. This character is a bit of a throwaway character but I do have the option of bringing her back later down the line.
I've just given the MC a part-time job too, there will be a few more throw-away characters here that the player can choose to interact with or not without affecting the main story but gives the option of quick sex scenes.
I will say this is probably ok. Like, having spicy scenes early is important for retention. But it can be perhaps a previous connection, someone established as already close perhaps.
But here's something I want to add for the "throwaway" characters. Maybe make them optional?
Some people want early sex, or frequent sex. Some people don't. If it's a choice you can make, then both parties can be happy.
I know it sucks when not all of your content is viewed by everyone, but if you're seeking to cast a wide audience net, and not be generic, you might have to accept that not everyone will absorb 100% of your content. Just make sure the content that is there to be absorbed is entertaining, and I suspect your work will do great.
Just a heads up, it's incest based in case that's not your thing.
And a side note, a ton of people like incest; so you're not going to be without any readers. If it's key to your story, then awesome. If not, you could always make that a choice the player can make too.