Kobe Bryant did not become an elite player because he practiced more.
While I agree with what you say about mechanisms, this bit isn't true at all, and nor is the gist behind it. It takes an immense amount of effort to reach the top in anything. And effort makes a large difference even for people on lower levels; but most importantly, that difference could be colossal, except that it has to be channelled properly for this to become reality. You can't just "work more", you have to figure out how to work in order to improve.
Although of course mechanisms are extremely important, so I would recommend them also to the OP. As for your friend who only studied partially for 2 days, maybe your friend has simply been putting in a consistent and fair bit of time every day throughout the year, which is why his overall mastery is better. Grasp is the only thing that leads to 40% mark differences. If it was knowledge, well then you just need to make sure to learn things properly ...
I wish Big Daddy were correct. I wish that I could beat Usain Bolt by better or smarter practice. I wish it were true that everyone could earn an "A" by just studying harder or longer. I use my own experience as a guide. I definitely did not study very hard in organic compared to my other classes, but I did not have equal results. I wish organic chemistry were an easy class and low achievement was due to a lack of or misplaced effort. I suspect that is simply not true. My book is virtually how I studied, but from what students have told me, many of them have studied much harder than I did.
If there was a skill that a class had to master, I would expect a bell shaped curve in the mastery of that skill. None of this should matter. Your achievement is independent of everyone else's. If you want a high grade, you will have to work for it. I don't see how it matters how much someone else studied.
Yes. You will not beat Usain Bolt. In the same way, the average person will find it difficult to become one of the greatest in the world. In the same way the greatest in the world cannot reach that place without an enormous effort. Kobe Bryant did become an elite player because he practised more; he might have been better than someone completely average even without practice, but to reach the top you need the effort as well. Talent alone won't succeed.
In any case there is a massive difference between "working harder" and "working better". If I have a certain, rare, key insight into how to think about, say, writing music (or virtually anything else that resides in the mind - the argument is harder to apply to physical aspects but you could still try), and some talent, I might well become a musician like Mozart; what another person who is only just above average would have to do to join me on my level is to gain that insight into the nature of music, not just "work harder". Gaining these insights is a matter of thinking clearly about what you need to do and how people have done it in the past. It is not impossible. Musicians do not just "write whatever comes to them" (at least, Mozart didn't); they write about what sounds best, and their insights govern them.
So to relate this to organic chemistry: skill comes from realizing how to understand organic chemistry at its core. If someone gets
vastly better marks than you, it is most likely because they understand what is needed at a deeper level, and to rectify this you must rethink the way you see organic chemistry and the problems before you.