God you're quick, are you on this thing all the time? I just refreshed and there you were!
I really don't think I am misunderstanding you at all.
You said that a parent is entitled, indeed should, put their lover/current partner/spouse above their children. I think that in practice, that would mean the children who were not also current partner's children in such an arrangement would come very far down the pecking order. That could be your child one day. It would not be acceptable for that to happen to mine.
You are a stepmother, and write from a position of knowledge of what that is like. Fortunately I do not know. But I am a stepchild, and it is shit. And for 99% of other people whose parents remarried that I know, it is also shit. You are never as important again.
Now I anticipate that you will say my views are coloured by my own experience, and in that way attempt to dismiss them. So are yours, and no less relevant for it.
For the OP, I think that you are not being unreasonable, it is understandable that you do not love this child or feel that her father should put her first. But fortunately, he does. If you are unable to make your relationship work on terms that are workable for his other family, then you need to find someone who can give you what you need, it sounds as though this man can't. I do appreciate that that is hard for you and I do feel great sympathy for your situation.