I mean they have mutual feelings in the end (I think?)
No. I am pretty sure you are the only one who read it like that, judging by this thread. I am personally of the opinion there are not even one-sided feelings in play here. The one who raped her friend did not do it because she harboured secret romantic feeling for her, but because she was obsessed with her friend "being left behind", which in terms of this story means "not experienced sex yet". Main character's happiness at the end was because her friend is no longer a virgin, not because she was the one who did it with her. Happiness which she intends to broadcast to everyone. "Look, look, my best friend is no longer a virgin, how awesome is that." Those are not "feelings", that is sheer insanity. And you do not even have to 'read into it' to interpret it this way, since the author literally wrote it like that.
The friend that got raped also did not express any romantic attraction towards the main character, or anyone else, at any point in the story.
I don't know why you guys are making a big deal out of nothing
Rape (and a pretty insanely-motivated, at that) =/= nothing. It is only natural this kind of story would generate discussion on the subject, it would be strange if it did not.
I'm pretty sure a yuri manga that has a het ending is way worse than this *cough Happy End *cough
Personally, I will take a het end over a badly done yuri rape. Emphasis on 'badly done', I am not against rape being used in literature/media, but in this case it was done completely nonsensically.
Also, regarding het, you seem to have missed the fact the main character looks at her het experience as something positive, a social triumph of a sort, and also genuinely thought it does not count between girls.