I think it is even worse -- the inflation is not universal. At Cornell (undergrad), most engineering classes set the mean to B- or C+. You had to go 1SD higher to get to A- and near 2SD to get A+. Imagine how shocked I was to hear my friends at Princeton had a mean set to A-. Consider the pressure this puts on some students and not others, esp when you're all applying to the same graduate programs. Is a Cornell B+ worth more than a Princeton A-? Statistically yes, but in reality no one is harmonizing the distributions.
There is also the issue of fancy private prep schools which have 10 or 15 "Valedictorians" which many of us public school students were shocked to learn when we arrived at college. You'd meet multiple people claiming to be valedictorian from the same school's graduating class until you learn that private prep schools stretch the meaning of valedictorian.
Some reason life lessons: pay enough and you get to bend the rules.
Some reason life lessons: more elite, less pressure.
All three of these things are already happening.
For example, the Cal State University system has purely objective admissions for most campuses. That's good! But while they technically consider SAT scores, the last time I looked the difference in admissions points between a minimum SAT score and a maximum SAT score was roughly equal to the difference between a 2.0 GPA and a 3.0.
I personally prefer the GPA system as it measures your performance over your final 2 years of high school rather than having your future determined by one test.
In the US now we have federal school testing to try and normalize schools better. But before that many schools were graduate students that were illiterate (actually some still are, but I hope it's gotten better..). The US is 10x the population of Canada so image the difficulty for a liberal arts school in the northeast looking at a student from some rural 500-person school they've never heard of from the southwest.
Canada's population is smaller but we also have many obscure rural schools. Non-prestigious universities don't have much data but they also don't have much choice in top applicants so it doesn't really matter. Over time, they can build up decently accurate profiles of high schools for majority of applicants.
It also puts you at a disadvantage if you come from an immigrant area or poor area where your 90% will not count as highly as someone with 60% from the richest areas with a trackwork of success.
It really punishes anyone not rich and locks them out of elite universities and pushes most of the poor out of average universities.
A single test where everyone can study and pass seems more fair than basing it on things that can be impossible to change like where you grew up
Neither system is perfect but I think the purely SAT approach creates too much unnecessary stress for high school students when there are other proxies for determining future success.
There is nothing stopping you from taking the SATs multiple times. It's encouraged because you most likely will go up a few points the 2nd pass. I've taken it twice myself, 3 times if you include the PSAT. And I also took the ACT, only once.
GPAs you can only screw up once. If you fail even one class it's impossible to climb back to the top.
Grades can be easily biased