My family know that I have no preconceptions of how a grandparent is supposed to behave, as mine were dead before I met them. So grandparenting was new to me.
If I know my grandchildren want something, I help them get it, either by buying or by giving money towards it if I can. I don't analyse too much, and neither do my kids. They just accept how I am/ we were.
My husband was good at music, but his parents discouraged it, so when our sons were born, we said that if they wanted anything to do with music, we would provide it if we could.
We treat the grandchildren the same.
My grandchildren have not grown up to be grasping children, just wanting things for the sake of it. They are really nice children, thoughtful and kind to others, just how we want them to be.
If either of my sons were like the one in the OP, I would be most upset, too, and not at all understanding.
Their father died nearly five years ago. We keep up the traditions that we started as a family, and one of them is probably buying too many little things, giving lots to unwrap.
It doesn't fit in with our conservation policies, but we make sure that all the paper is recyclable.
Christmas is supposed to be a time of giving, not a time of controlling other people.
Probably said too much, but who cares; it's Christmas.