Caveat: I have not read the whole thread and responding to the general question "Grades and success?". I do apologize if it is irrelevant, but I would like to share my opinion on the subject.
When I was younger, I was deluded by the fact that grades were essential. Of course, I was also interested in the subject matter, especially when it came to languages and social subjects, but I was obsessed with grades. Or I thought I was. Later on, when I was a bit more mature, I came to realize that I was not obsessed with grades; rather, I was obsessed with success, which I sought in grades as an (naive I know) objective appraisal of my abilities!
At that time, good grades were my way out of a desperate situation and into a better condition where I could achieve my dreams and goals.
Of course now I realize that grades are completely subjective, not really indicative of future success, and actually quite arbitrary, as is the reputation of the institutions I attended. If I could speak to my younger self, I would have advised against obsessing about grades and tell myself to focus more on long-term learning. Then again, this concept begs the question of whether or not I would have achieved enough to get the scholarships that were my ticket out of the country and starting a new life.
Let's face it, folks: It may not be accurate, true, or even fair, but this world revolves around some kind of measurement of ability, even if it is not really representative. And in this world, that is the grade, the stamp on a document, or the recommendation from a professor or employer....