If you decide to argue that good test scores favor the rich because they can afford test prep, why are grades allowed at all? In reality the bar to afford 10 on

If you decide to argue that good test scores favor the rich because they can afford test prep, why are grades allowed at all? In reality the bar to afford 10 one hour sat prep classes is much cheaper than 4 years of tutors in different subjects. And, since I have no doubt that'll likely occur eventually, what would we use to decide who gets into colleges? Is it going to be a competition on who tells the best story in their essay? Can you even be held accountable for lying in the essay, could you even prove it? What else is there?