I partially agree, but I also disagree that it’s all about profit. The point of revenue sharing is that if they make the engine well, then it becomes more likely for your game to be successful. That revenue share can be re-invested to continue improving it.

Would you say that the engine is not part of the game? In what way is it seperate from the thing you created? Employees ideally should get a share of revenue, as they helped create the product, and the engine is part of the product, so their employees should get a share for the work they helped create as well.