I understand your feeling and I can reassure you now that it comes from the fact that your path to corrupt the characters is limited to a single succession of events (Alice's example : go to school, do tutoring, sleep), which makes it linear. When you have several activities to raise influence for a single character, I'm pretty sure the story for that character will unfold in a better way.
I don't agree with the game being grindy as you say tho, you can get all the content of a character before even reaching Sunday. Or maybe I misunterstood what you meant.
Thanks man and rest assured, that's just because it was a preview release. More build-up is coming