Carol is the main girl. At least, that's what can be seen from the way you've written it. She is the character that has the most time (besides maybe Rachel) and has the most relationship progress (discounting Roxy because she started at Sex and is trying to move beyond it).
We can agree that Carol is the "main girl", but it's still clear that you chose to pursue her. If you don't "love" her, you're free to not pursue her. It's like you made the choices to love her, but then you went surprisedpikachu.jpg when the MC said it.
Ashley, Yuki, Sara, and any of the others are currently at "Minor Character" status because there is so little interaction with them. So all things are not equal. You have made it clear in the early game that Carol is the main. Whether that was intentional or not, that's how it is. There are not chances to flirt with Ash or Yuki like there is with Carol. You don't spend hardly any 1 on 1 time with any of the other girls like you do with Carol.
Why does it matter if they are minor characters? Why must everyone be equal? I don't understand the logic.
You centered her in the middle of all events in regards to the other girls. With the exception of Hannah, Roxy and Rachel, you meet every other girl through Carol which makes it be that the only way you'd be introduced to those characters is if you already had a good relationship with her.
So with the exception of 3 girls (Hannah, Roxy, Rachel), you meet 3 other girls (Ashley, Yuki, Sara) through Carol because they are her friends. That sounds reasonable to me. And I tested the game just now, you'd still be introduced to Ashley, Yuki, Sara even if you only have 1 point with Carol (which I think is the minimum because you can't be 0 point at that time). So point-wise, there's nothing that forced you to build high points with Carol to get introduced to the other girls. Story-wise, the introduction is more because Carol is a nice person trying to introduce a freshman to her friends, and not necessarily as an extension of MC's relationship with Carol.
If you had written it so that the MC met the girls himself individually, had equal time with all of them, had chances of having the same number of points with all of them, then you could say that the game is balanced and Carol is not a railroaded choice. But that's not the case. In the current game, you are pushed toward a relationship with Carol almost entirely, and there is no semblance of a relationship with the others as of yet, due to the lesser screen time.
Once again, why must everyone be equal? I really don't understand the logic. I get it that you might not like the main girl (Carol), but there's literally nothing in the game that forced you to like her. "Not liking Carol" is a completely separate topic than "liking a minor character who doesn't have a chance to shine yet", and it feels like you're trying to force them together which is very very weird.
To me, the moment you made the mistake was when you had Carol invite him to the girls' room and played the game. First, introducing the other girls like that made them dependent on Carol as a proxy. Secondly, you shortened that Game Event to the point where the most you could gain with any of the three girls is +2, but that's only if you concentrated on one girl. If you had let the game play out longer or had allowed for more questions to be asked, there would have been at least 3-6 points more
First, it's proven that you don't have to be in love with Carol to get introduced to the other girls. Secondly, the points are irrelevant because they can be assigned as needed (ex: you need 7 points for Carol in the hallway, but you only need 2 points for supporting Rachel) so that there is no need for Ashley/Yuki to have 6 points instead of 2 points.
You keep on trying to imply that you have no choice but to love Carol. It's simply untrue. If you don't like Carol, then don't pursue her. The options are there. You chose to not take it.
