I think you have a misconception on the concept of a game dev milking its patrons. Most of points you make is more a criticism of the game rather than evidence of milking. So let me cover you points.
It sounds you don't enjoy how Siren prefers to have things progress to sex. This isn't done with every character, but if you don't like it then that is fine. You are free to dislike the game, but that is not evidence of milking.
The only games to have a Christmas event are House Chores and Town of Passion. An both of those events are very different from each other. I will admit the outfits for Mary and Linda are very similar. But then what did you expect from a Christmas event. As for Halloween only the Zombie Retreat games and Town of Passion have such a event and each one is very different from each other.
To my knowledge this has not happened in any of Siren's games. An even if it did it wouldn't have an effect on his output since he doesn't produce any of the art for his games.
While I don't always agree with Patreon policy, it is one of the larger more famous platforms for developers. I know Subscribe Star is a thing but it is not as well known as Patreon. Which is why many devs choose to tip toe around the issue of incest. In Siren's case you can pick what roles you want. This works out well since you can still go the incest route if you want to and not have Patreon shut you down. In my opinion that is not evidence of milking.
So you want Siren to put emphasis on existing cast rather than on adding in new characters. Fair enough that is a valid criticism. But I don't believe this is evidence of milking. Having a large or even expanding their game does not mean that Siren is trying to milk is supporters. After all the more characters he adds the more he has to pay to his artists for creating the new characters. An unless it draws in more support that will be a problem.
So in short it sounds like you just don't like the game. Which you have every right to dislike it. But just because the game doesn't meet your tastes doesn't mean that the dev is trying to milk/scam supporters.
Suppose it's my fault for trying to reason with a hardcore shill of Siren games. Or you work for them, idfk.
He's certainly not so transparent about it like say, Milfy City dev. But adding a random character and slapping an above mentioned template on it IS very much reducing your workload and pretending like it takes a long time to make. That way you don't have to develop existing characters and their relationships between each other but just make a new one and have them repeat what every other character did before them.
Stacy in ZR2 having a new spot where you can have sex with her isn't actually anything new, it's the exact same copy pasted shit.
Pool Party in ZR1 was beyond disappointing and at least I see people pointing that out as well.
House Chores recent update was literally 1 fucking scene and an outfit.
Not to mention all these bitches look the same. Slap a new hair and an outfit and you've got a brand new character. Wow!
The fact that anyone would make excuses for Siren really annoys me. Why do you people refuse to see what's so obvious? Are you all donors and lie to yourselves? Every single fucking dev in this business is purposely delaying the work they could release sooner. I wouldn't mind if the content wasn't fucking trash.
Think I'm fight a losing battle by ranting on a porn site tho. I see people defend Summertime Saga dev as well. That guy is without a doubt, the king of doing fuck all and still be on top.