I agree with you. Especially considering unless you read this board, or read the tickets for the party, you have no idea that they will let them in 3 hours early. During the day, the loudspeakers only mention 7pm, so that is how most people would plan... again, unless you read this board or look at the actual party tickets.
So technically even though they open the park 2 hours earlier, you lose the last 3 hours due to the quantity of party guests arriving and flooding the lines. I didn't check, but maybe they also can use up the fast pass system as well for the last 3 hours?
I'm not certain if I will attend on a party day again, but if I do I'm going to check how they monitor people entering the long lines such as Space Mountain at about 6:45. I'm curious because those guests would not leave the park most likely until well after 8pm.
BTW: I have not heard back from Disney from my e-mail yet. I had expected to, but maybe they are getting many many e-mails these days. If I don't hear back I plan to send them the same wording via snail-mail. I just personally feel they should at least explain why this occurred. Last resort is through the City of Anaheim to verify restrictions of restrooms. Maybe they can close them all at any time or leave just a single one open for 50k people. I just don't know right now.