So are you arguing against having letter grades or for? I will provide an answer for both.
Why schools should get rid of having letter grades:
Letter grades are unnecessary and to unspecific when it comes to upper level school. For example, when in high school, you have a GPA, your percentage in each class determines that GPA. Having a letter grade is useless because that’s not what your GPA is based off of.
Why schools should keep letter grades:
It gives you an overall understanding of your grade instead of a specific percent. You can look at a test and know you did well from just seeing one letter instead of a percent. This is best when teaching lower level students such as first grade because they most likely haven’t learned about percents yet.