I wouldn't compare anything about Idoling to AKB, the way AKB is right now is very unique case, the AKB fanboys will support them even if they all had boyfriends.
Idoling fans are a bit more sensitive, quite a few have already left because of how 5th gen. audition voting scam...I mean scheme came down.
I think Fonchi has been contemplating quitting for a while, the more sudden graduation to me was Yazawa, and how she still seems to be around Idoling tells me that her departure clearly was premature and not of her own will. But really, does anything Yazawa does surprise you anymore? She's the exact definition of a "loose cannon", I wouldn't be shocked at all if she was going wild around boys and the management finally said enough is enough.
Back to Oji, yeah I also clearly see that her facial expression and demeanor on stage is very unprofessional and her heart is not in Idoling. What bothers me about Oji is how she seems to have this animosity towards Idoling members from the very beginning, maybe it's just her rebellious nature or puberty, but she needs to realize that as the wise old Kato used to say, the true rival is outside Idoling, not within.