I do understand this sentiment and I think the popcorn-movie comparison is apt. It's just... there can be so much more. "1Room - Runaway Girl" has a very short but cute story and its decently written. "Accidental Mind" has a great story as well. Even very fantastical stories like "Headmaster" can have crazy things happen without stretching my suspension of disbelief too much by simply taking the time to show how you can go from a normal world to an "ecchi" one.
I think that's what's bothering me most about it. There's clearly talent and effort that went into the very cute artwork for Summer Memories, as well as the overall game flow, but then the devs dropped the ball hard on story and characters. The loss isn't a minor one either IMO, because good writing makes the fantastical lewd stuff more erotic than just "Oh, I guess we're having consequence-free sex now!" Where's the tension and guilt after Rio starts her younger cousin's sexual life? What if Yui's motherliness was amped up, and her scenes start more intimately than rudely waking her up with a titjob? Have Miyuki's self control start to slip as she boosts her ego by teasing her nephew? Taking a little more time to develop these stories and characters adds more context to the sex, which is what makes a game's potential so much higher than an ass-blast of porn gifs or some shitty JAV. Why are these characters having sex? Don't care, doesn't matter, press LMB to cum.
I completely agree with your standpoint, the big selling point of most hentai games besides tits ofc, is the downfall of the characters morals into their lust, then at the end become what the MC is. My favorite part of this game was the slow subtle influence the MC had on the girls. I think it progressed too fast for some of them. I liked the slight guilt Miyuki had in the beginning.
I was most concerned with winter memories story foundation with how all the girls will remember you, even sub-heroines will. Kinda ruining the subtle influence and most of all the moral secret between you and the girl you chose in the last game. (No idea how he had the time to do all those things to all the girls within one month)
Personally I woulda liked it more if you could chose what "girl or girls" you wanted to remember you in the beginning so you can still develop that hidden connection.
I'd then enjoy it even more if once you finish that play through of a logistical story you can unlock slightly more unrealistic new games+. Where all the girls remember you, playing into that unrealistic fantasy.
Overall, yes I think making all of them know you in winter memories slightly ruins the believability of the fantasy. Still gonna get the game cuz the DEV made a very replayable game and the sequel will be far superior