You're right that it was much shorter and didn't have much of an arc - I would've loved to see more happen in the routes with some of the subplots introduced in the previous game, like Lucette's relationship with her father, or more of a focus on the Tenebrarum and magic (I haven't played all the routes though, so maybe other routes have more). But, Evermore does specifically say it's not a full sequel - it's marketed as a fandisk, so there's no point in expecting it to be something it's not. Since it's still in development, maybe the devs might add more, which would be awesome, but they also might not.
Also...we got Cinderella Phenomenon for FREE. I would gladly have paid $20 for it, so the $10 I paid for Evermore feels like I'm paying the devs back for the amazing job they did on CP.