Yes, it is more complex than that.

1. It was that the UK was saying the Ohio valley, which the entire NA part of the war was over was off limits to the colonists.

However, the UK could not have won the war when they did had those native groups not changed sides to ally with them. Given the dire state of the UK finances, its questionable how much longer they could have fought.

That land would also not have been needed had the elite of the colonies not taken ridiculous amounts of land for themselves.

2. At least particularly to Pennsylvania, in the middle of the war; the Iroquois interfered with a treaty that would have seen the colony recognize the land held by the Delaware tribe in the Ohio river valley as Delaware tribe land. They(the Iroquois) did so because they wanted to be the only tribe to make deals with the English and would force the other native groups to work through them. This strategy is also why the Delaware tribe had been relocated by the Iroquois to the Ohio valley in the first place.