You're not quite seeing the point: This is not a developer trying to use their ecosystem for free, not in the OnePlus example: This is a developer saying "Thanks but no thanks, we'll choose a different ecosystem"

And Google inserts itself into the relationship between the business partner for that other ecosystem and bullies them into cancelling the deal.

Off course it's important to keep in mind that as of right now, we have only Epic's highly self-interested interpretation of events, and the truth may be far different. It seems LG for example had a pre-existing contract with Google to not do the sort of thing it was about to do with Epic.