This is not that uncommon for a story to portray, and I think people are feeling a bit critical when this is legitimately how a story is told more often than not, with unrealistic angles to fit its narrative focus. This is a fantasy, its designed to be what a fantasy is, as in its is not supposed to be what happens to you. You are not the MC, you are just living out an ideal outcome through his eyes, nothing about porn is realistic or even comes close to it.
MC has a few great things about him: He's the guy who has massive natural charisma (which is in fact a real thing), he's a star athelete, and he is a sweetheart to the core, and this in turn is allowing him all the other good things in his life. That's not so damned hard to believe, as it's totally what the fuck happens in real life even if uncommonly. Also the human male can support an erection every twenty minutes, and being nineteen and horny as fuck means he can keep going even if most of them would be more dry shots but that's artistic liberties. The amount of sperm a man can produce is massive so its not so far fetched.
We're built for sex, and a lot of it, because we're animals.
Sure all of this happening in nine days is a bit odd, but then again, who cares if its condensed? This is the inciting incident of the story, about how the MC's life went from living in a trailer with his step mother, to being the star hero to turn a failing college basketball team around and bring his school to the top of the list. Sure it adds banging a harem of awesome girls, but who DOESN'T wanna fuck the basketball superstar who is literally the hot topic of the country in terms of college sports?
Bonus is that he's a sweet and caring soul with massive empathy and issues with letting others own, which is something I relate to personally.
Unrealistic? Somewhat yeah. Entirely unrelatable? Not a chance, it's very human and still a lot more believable than most porn out there and still manages to be a lot more slice of life that I think its given credit for.