GPA as a metric is terrible because there's no standardization of grading across schools. At best, you can use it to compare applicants from the same school, and sometimes even at the same school Professor Birch is a much harsher grader than Professor Elm, so comparing grades of students that took the same course but from a different instructor is tricky.

Standardized tests have difficiencies, but at least the scores are comparable.

>It still is a very useful metric.

Maybe for lulz/curiosity, definitely not when it comes to accepting somebody into college.

How to compare GPA of people who didn't gave a fuck about "lame"/"easy" subjects and outperformed at maths, physics, etc

with people who didn't outperform at e.g maths, physics, but were putting effort into the lame subjects?