Ok. Now fix the system in a timeframe that is compatible with your expected working life.
That's the problem with the quote. Grades may not be the most important thing but they can, and often are, the most important thing for any given individual. For every Bill Gates that dropped out, there are a million John Doe's drowning in student loan debt with no degree and limited future prospects to show for it.
Who are you asking to fix the system, and why? Me, maybe? Paul Graham? gofreddygo?
How is the thing you say a problem with the quote? These can both simultaneously be the case, and often are:
1. The most damaging thing John Doe learned in school was learning to get good grades.
2. Richard Roe didn't get good grades and is drowning in student loan debt with no degree and limited future prospects to show for it.
You have offered no reason to believe that if (2) is more true, or true in more cases, (1) is less true, or true in less cases, or less important. In fact, this tighter conjunction can also often be true:
1'. The most damaging thing John Doe learned in school was learning to get good grades.
2'. John Doe didn't get good grades (despite being damaged by learning how, he didn't learn how enough, or other things interfered) and is drowning in student loan debt with no degree and limited future prospects to show for it.
You've also offered no reason to believe that if (2') is more true, (1') is less true or less important.
I have an idea! Maybe you're misinterpreting the quote as meaning that, if you're in school, it would be a good strategy to stay there but not learn to get good grades. In that case there would be a sort of conflict: by diminishing the damage from (1') you may be increasing the risk of (2').
But that isn't what the essay advises at all, and I'm puzzled as to how you could have read it as suggesting that. It explicitly advises students to do exactly the opposite; it advises them to get good grades by hacking bad tests in the usual ways (cramming before exams, etc.) because everyone will judge them by their grades.
But that's not really the point of the essay, and it would be a pretty boring essay if it was. The point of the essay is its advice to people who aren't enrolled as students: unlearn how to get good grades, and instead of focusing on how to make your product look good, actually make a good product. Also, and maybe more importantly, try to work in fields of endeavor where the way to win is to do good work, rather than hacking bad tests like you do in school. (This might suggest not going into school at all, which would at least avoid the student loan debt problem.)
That's the problem with the quote. Grades may not be the most important thing but they can, and often are, the most important thing for any given individual. For every Bill Gates that dropped out, there are a million John Doe's drowning in student loan debt with no degree and limited future prospects to show for it.