I have to say you are very well informed and aware of the GMAT test background and elements (diff tests having a deeper/shallower pool). Kudos!
There is obviously a bit of a question as to why you are diving into this question and its practical application (I can tell you that there are probably 10 people on GMAT club such as
IanStewart and myself included, who can spend hours talking about the theoretical aspects of the GMAT and not get bored) so I am totally comfortable leaving the practical application of this question tucked away for now.
I would generally agree with your analysis. I have noticed on my real test and also in the practice GMAT Prep tests that the difficulty is not constant and it fluctuates even if you are doing well. I have a number of theories about the GMAT, and they are all mostly about optimization and building a CAT test efficiently in such a way as to minimize the cost and effort of test writing since people can take the test every 15 days. Having to create a database of thousands or even hundreds of questions would be too burdensome and difficult. Moreover, creating a new database of HARD only questions for those test-takers who can score a V51 and a Q51, would be even more wasteful since there is just 1% of them. The main mass is in the middle of course and thus the best bang for the buck would be writing as few diff questions as possible and recycling them as much as possible (let's touch recycling as that will take a whole separate page and that's not the point of this discussion).
So, as you very aptly pointed out, a test with few hard questions and generally a shallow pool of questions will serve a good test-taker mostly medium diff questions but will require a larger number of correct answers than a test with mostly difficult questions. Thus GMAC has a few ways of dealing with high scorers - they can control the pool of questions and give them hard questions or they can use a shallow pool but be much more punitive with mistakes. (I am not saying this quite perfectly but I think you understand what I mean). There are many levers available to test-creators and also having experimental questions that are not graded is an additional layer of obscurity that makes some of these evaluations harder and understanding one's performance during the test potentially a pointless task (which smart people say take it one question at a time).
Easy vs. Diff Questions.
To start answering your questions, you are correct - being good about solving easy/medium questions is the path to the high score. People mistakenly chase hard questions, thinking that if they can solve them, they are guaranteed a high score, only not to see more than 1-2 of them on the test.
Quant:I had only one hard question (which i failed to answer correctly) on my test. It was a probability question which was not that hard now that i look at it, but I was not prepared for probability. I spent 3 mins on it, and ended up guessing wrong, and move on. I got Q49 despite that wrong guess, just 2 points short of the max score. All the rest of my questions were medium and easy diff on the test. I clearly made more than than one mistake but in my opinion none of the questions I was tackling were hard... though twice! i solved a question only to see that my answer was not listed among the answer choices. Twice on the real test i was lucky not to have a match. I messed up up under pressure. Everyone does and mostly on easy questions with just simple gotchas. If you can be good at those and not caught caught up in the panic, you can get at least Q49 without ever touching a hard Quant question - I clearly have proved it on my test.
Verbal:I got V42, which is still 96th percentile. It is not V47 or something super high, but in terms of difficulty, you are almost at the top already, so likely I have made a few more mistakes than I should have (unfortunately no ESR in my days). I can't tell you if the questions were particularly hard - it was really hard to judge the difficulty level because I felt I was guessing every question. I was just barely certain in my answers and if I had the time, I would spent hours on each question but I had to pick an answer and move on, which I did. For about half the verbal section, I felt I was failing. I had no confidence in my choices/answers, they just seemed slightly better than the others but not necessarily right. Many people who score well on Verbal report that they felt as though they were guessing, which those who get low Verbal scores, often report they felt very good about their answers and were pretty certain.
Difficulty in General:I looked up the hardest and easiest questions on GMAT Club and found that there are few Official Questions in the Top 100 and quite a few in the Easiest 100. That's 100 out of thousands of questions here, so in general the difficulty of the official questions is not high, which confirms the concept that GMAT probably does not have many hard questions and difficulty sort of bobs around medium/hard/medium for even the top scoring individuals, likely because of the question pool lacking sufficient number of the hard questions.
https://gmatclub.com/forum/150-hardest- ... 04134.htmlhttps://gmatclub.com/forum/150-hardest- ... 04136.htmlI assume you have seen this big back and forth discussion that is quite interesting:
https://gmatclub.com/forum/q51-v50-253258.html It talks a bit about one of your questions related to Verbal Difficulty and how could a person with all answers correct get only V50? (their score got updated to V51, but it stayed at 790).