Pivotal. It really depends on what was taught in high school.
Gre level math was taught till before grade 9 in india. Starting 9 to 12 it was mostly calculus. So it’s easy for people who went thru those school. On the other hand history/philosophy/humanities is crap/non-existent in those schools. So it’s just a matter of what was taught when. That’s all
One of my buddies attended MIT for his PhD and he didn’t break a sweat in his core curriculum and made perfect grades in his coursework. My buddies who attended lower ranked schools (top 10) had similar stories to share. That being said, doing original research is hard and that’s when things get challenging. The faculty in US engineering programs (top 10) is outstanding. The honors for science goes to European countries. Folks from the Russian block are stellar in pure math— no other nation comes close.
I don’t need to troll. I was lucky to be surrounded by classmates who were brilliant academically and in many other ways. I see people bragging about TC, LC and GRE scores. My classmates bragged about getting checks from Donald Knuth for $2.56. I clearly remember them taking the GRE sample tests without pen and paper and getting perfect scores.