One of the problems of High School GPA, compared to college, and then, further on to grad school, is that each focuses on an increasingly narrow set of academic subjects, which is understandable, however, this does not reward the students who are really talented in those fields.
Basically, the system is set up to produce specialists, but recruits generalists. You would expect the top graduate programs in math to look for the best kids in math. However, to get there, one first has to be accepted to the best math undergraduates programs, which are inaccessible to kids who aren’t also very good in everything else. So even if a kid is a math prodigy, if their language and history, and biology skills aren’t that good, their GPAs and SAT scores will keep them from many, if not most, of the best undergraduate math programs.
Since academia is as prestige-ridden as anybody here on CC, the top math graduate programs will almost never accept a student with an undergraduate degree from a “lesser” undergraduate program. Moreover, not having the resources that a “better” math program has will also stymie the development of a top student, putting them at a disadvantage, relative to a student who may have less talent, but has had many more opportunities and resources.
This is true for almost every field.
By allowing for a range of SAT scores and GPAs, colleges can accept kids who are really good at a small number of things, but weaker in others. Great writers who are bad at math and math-based sciences, physicists who don’t do well in the social sciences, etc.
Then there are kids who do not do well in high school because the way that they are taught does not work for them. Because of things like NCLB, and other standardization, kids who think differently are often at a big disadvantage in high school. Many of these, though, do much better in a college setting.
Finally, all that GPA actually indicates is the ability to do well on exams. Since a very large number of these exams require nothing more than memorization and regurgitation, many of the more creative and inventive minds get lower grades. These students are not encouraged or supported, and rarely attend the colleges with the best resources.
I think that, as competition increases to get into colleges with more resources, and there is an increased reliance on GPA and SAT scores, the quality of research, and of researchers, will drop.
An A in history says that a student is able to remember what they learned in class, usually memorize dates and names, and repeat the analyses done 30 years before. The kid who is able to perform a new and deeper analysis and puts that in, instead of what they learned in class, will not get that A+.
In most high schools, kids get As by doing things the way that they were taught. However, innovation and creation are achieved by not doing things the way that they were taught.
The major achievement of limiting access to college to kids who get all As and top SAT scores is reducing creativity and inventiveness in those colleges. Since those colleges tend to hire from themselves, in many fields, I expect that this will hurt them in years to come.
Many of the math and science Olympiads are driving STEM in the same manner - they don’t really reward innovation and creativity anymore, they reward speed and repetition.