MCAT correlates least I'd say. Step 1 is purely what you know. MCAT you can get by with being a good test taker/strategy.
I agree that MCAT is easier to get by w/ strategy vs step 1 but the nature of the test is different. If the MCAT is ALL bio then the story would be similar to step 1. On the other hand if the MCAT is ALL physical sciences then those who have no good foundations in it will suffer. The foundation is easier in bio section as it is memorization, I will give me view later in the post. The foundation is the difference in why 1 is easier to prepare for than the other; you can logically figure things out in physics if you have a solid foundation (which doesnt require much memorization but good logic and understandin of basic laws of nature). All in all, these tests both require strategy and thinking but the nature of it makes step 1 require a lot more time than the MCAT.
Generally those who did well in MS1/2 put in a decent amount of time and likewise would put in time for step 1 so there's a correlation there but it's more so the 'hard working' component. Of course the more you study the more information you can retain, our brain retains information via many different ways and one of them is repetition. Step 1 score also of course has a correlation with MCAT, SAT because all of these test requires some component of intelligence. Those who are more intelligent are better at integrating information than others and memorize faster, n likewise those who are not can spend more time and retain the same amount of information with a lot more effort.
So effort, hard work and time plays a huge role in how well you do on Step 1. Intelligence definitely plays a role too like i said before, those who are smarter links things faster and finds ways to memorize things easier and see the big picture easier (physiology for example; is it easier to brute force memorize something or learn the mechanisms and the logic?). Nonetheless hard work is the most important so time spent is really important. There's a lot of thinking in this test but without the knowledge and foundation which unfortunately requires a lot of memorization, one cannot use his brain to think bc there's nothing to think on.
Another thing to take into consideration is the mentality of students. Some may say that MCAT is the most important test for a person who wants to get into medical school; but look at the grand scheme of things, many people will say that Step 1 is way more important as it is such a crucial factor that affects what road you will take on as a doctor. (38 MCAT, 220 Step vs 28 MCAT, 250 Step). Yes MCAT is important but once you get into medical school that has no bearing on residency; someone who scores a 240+ at a no name school (lets say ranked 100) and someone who scores a 220 at a top 10 school given that the other parts of the app/interview are similar, the residency will take the 240+. Many people realize this and study a lot harder for the Step 1 compared to the MCAT (I know the effort I put in for step 1 was way more that what I put in for the MCAT). The magnitude of this test makes most people study extra hard so it's not reliable to compare this to MCAT. If people put in the same amount of time they did for step 1 for the MCAT, I'm almost sure they would've done way better on the MCAT, I know I would've.
I didn't put in enough time for MCAT (I did get 99 percentile on the physical science section which was less memorization and more thinking, I barely prepared for it bc to me it was so logical and came so naturally; I did a little lower on bio which required a foundation that is more memory intensive than physical sciences... you cant really figure out which reactions happened for some orgo compound unless you've memorized/learned them, it's not something you can entirely figure out from scratch like physics which has logical laws/rules) bc i didnt put in the time for bio, I scored lower than my physics section. My foundation wasn't as strong bc the foundation for bio requires memorization (=time). On the other hand I put in time for step 1 and scored pretty decent, > 1 SD above the mean.
All of these tests require you to think, the only difference is the foundation, Step 1's foundation is memory heavy, MCAT is less so; and the less memory heavy the easier it is to do well with less time spent. MCAT is way less memorization and the time spent is not nearly as much. For Step 1, I spent ~10 hrs/day for 4.5 weeks of studyin that's 10 x 7 x 4.5 = 315 hrs. The MCAT i took no classes and just bought a book and did some questions, I'd say max I spent like < 70 hrs total. If I spent 315 hours on the MCAT, I'm almost sure I would've gotten 3-4 points higher. Because of the intense amount of information we need to know for step 1, some people aren't down to memorize that much (they did it for bio of mcat but that's nothing compared to step 1's information) and think that logic can get by but there's no foundation w/ no knowledge, the foundation of step 1 is the memorization and you're crippled no matter how genius ur brain can think if you have no foundation; this is one reason why some ppl w/ high mcat scores score lower than their 'potential' step 1 score, they simply didn't put enough time to establish the foundation.
For those who think it's a memorization test, a large part of it is but a lot of it also requires thinkin with the information you know. You think someone who can regurgitate word associations can do realli well on the test if he cannot decipher what's important and think? I doubt it. If the step 1 didnt require you to think then all questions should be 1 liners but it isnt, ANYONE can memorize, but you know the best doctors are the ones who can solve the problems, it's easy to ask what's X? what's Y? more importantly is, how do you apply this knowledge? How fast can you figure it out, thinking is involved. How do you differentiate X from Y in a clinical scenario? it's using the information you have at hand and apply them logically. How do you know to use sine and not cosine for some angle calculation, it's using the information they gave u and applying it. Drug X causes this side effect? some ppl brute force it, a lot of them actualli can be figured out. what if we change this group on the drug, what happens to this and that, is the side effect worse or better, etc, this all requires thinking but u cant think if u dont know the MOA, the compound, wht the group that was change did, what does the new group do to the overall structure, etc.
This is my view on this, not trying to say I'm right but I think there's a correlation with all of these and that step 1 is not a memorization test (it is partially), if it is then anyone can be a doctor if all you have to do is memorize and there would be no such thing as Ddx (a Ddx requires application of knowledge and thinking)