“I’ve taken and passed both the SAT and the GRE, and in neither case did each have any bearing whatsoever on my college and post-graduate success.”
There are no “passing grades” for the SAT and GRE. They are meant to show college or grad school aptitude. Not surprisingly those who score a 1600 do better than those who score 800.
That's not necessarily true. I've known 1600 scorers who washed out and also 800 or below scorers who did just fine.
The tests are subjective and only measure how well prospective college and grad students can take subjective tests.