In regards to Ann, it was more than just that.
She would (and did, if you confronted her about Eric jerking off outside Alice's window) take Eric's side in anything and everything, over that of her own son.
Even to the point, that Eric can very quickly convince her to let her own son watch her having sex with Eric.
All that within a few short weeks of even knowing the guy...
If it had stopped there, just as being Ann's boyfriend and a future rival for her vag, then he wouldn't have been as hated. It didn't, and got progressively worse.
Eric was a poorly written, poorly thought out "Gary Stu" antagonist for a long time over development.
It was so bad, that even when given the tools to turn the tables on him, (and actually showing glimpses of potential story relating to the opening of the game) Patrons wanted him gone and never revisited.
XD
Eric would never have an "alliance" with Max. He wants Max gone, which is the entire point of him suggesting the military school, which then becomes Maxes fate if he doesn't capitulate to Eric's desires on all the women, or maintain his own influence on their feelings.
It's about power, and Max is a threat to that power for Eric.
I think the same regarding how Eric ended up being. He could have been a good antagonist but the creator made it too forced, in fact as you say the word of Eric was the law for the mother.
For me it should have been divided in 3 levels:
-Submissive
-Obedient
-Slave
In the submissive level which would be the starting one, while on minor things she would obey Eric she would still have quite a bit of willpower and she wouldn't let Eric do whatever he wants, even less lusting after her daughters.
In the obedient level that should have been the point where Eric could let Max watch him have sex with the mother and he could take many actions against the girls if they don't step over the line.
In the slave level Eric would have full control over the mother and be quite active in making the house into his personal harem. The mother just doing whatever Eric wants.
If it was well done it could have been very interesting, as a player you could have been helpful for Eric in which it would advance faster from submissive to obedient to slave but earning much more money from him and being able to purchase more skills sooner or train your current ones.
Or you could have fought with him from moment one, reducing the speed at which he advances on your mother relationship but earning less money and having to find alternative ways.
At the same time this could have had quite a complex relationship with all the characters and of course blackmail opportunities or situations that may be in your favor or against it. For example one of your sisters wants money to buy multiple things, this could be an opportunity to have a better relationship but if you don't have enough money or you don't find the chance then Eric would have used it.
That's more or less how I would have liked the game to be, of course it would have been even better if your sisters weren't stupid or easy to conquer.
