well, we disagree. it's ok
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it's what breeds interesting discussions, even if no one budges from their position.
unless we do a scientific research on it, we won't actually know the answer, and it's only perception and anecdotal personal experience. you picked outliers in your examples too.
most games don't do surveys anyway, so knowing the most popular character for each one is impossible. but citing one game is easy: My Bully is my lover. Gwen is best girl and was polled as most popular and she got the very first scene, and the game is still popular. Another is Companion of Darkness, Noel is the most popular, and she got the most scene early, and still now, and the game is at its peak popularity.
Slow burns for popular girls is definitely a thing, though. it happens in many games. and it keeps the player wanting for sure, if it's done well, and is coherent to the character's story and personality.
in Badik, Bella and Jill are not the most popular. i'd say it's quite equal, fans are spread among the girls rather evenly.
you seem to have a preference towards girls with bigger boobs, and milfs, which is totally ok, but it doesn't mean that they are automatically the most popular. though, those two "traits" are very popular indeed.
badik has scenes for all the main girls, and side girls now, and it's still popular and going stronger than ever. it is the exact counter example to your argument. each update gives scenes for all main girls at the very least, and many side girls too, if not all of them, depending on the update. that game uses both slow burns and quick scenes, and they make sense for each character.
Story and storytelling are important. yes, I, myself, put them at the top of my priority list for sure, but for the majority of AVN fans, they are still important. if not, then they would only need to go to free porn sites. People that only use gallery unlockers and never read a line of the story are rare, imo. I haven't seen one yet, but I believe they would not discuss the games anyway.
It's not just about the girls' model and physical appearance. their backstory, their dialogs, are also important to make them lovable and popular.
Also, if you say most people play the game for the sex scenes, then they should want even more sex scenes for the girls they prefer, wouldn't you say ? that also contradicts your own point.