This is actually something I'm fairly serious about so I'll delve more into what I actually meant by that comment. Was a bit brief I apologize.
I'll start off with your sources. The first one is based on COMLEX and I'm an allopathic student so I'm going to ignore it. Its also kind of oddly written, I don't understand why they don't give you the correlation coefficients for the results in the introduction results section at the beginning of the paper... But alas. The second one actually showed a fairly weak correlation between preclinical grades & getting at least a 240 on USMLE Step 1 (r=0.356), so I don't really believe it proves the point you were trying to make. Both studies also have a very small study selection (<200 students), where the number of medical students in the US today is over 20,000, so obviously I would point to a low power.
Anecdotally, I feel like the way that medical education system is set up right now is inherently flawed because there's no fluidity, at least at my institution and the other institutions my friends are at (n=5). You might have 5 people giving you a COPD lecture and bringing out different facts (Histo, Anatomy, Path, Physio), that they feel are important. As a result for a student you often times don't realize whats actually relevant or important about that organ system, so when you get to dedicated you're forced to basically re-learn the material from a clinical and USMLE standpoint.
Obviously you could say that you should be doing questions on the side, but the point that you're trying to make right now is that you shouldn't need to, as long as you work hard during preclinicals and do well in your class exams that should be enough. But in my experience it can be, but at the same time it can also be a difficult road to walk if you're not someone who inherently picks things up quickly.
Lucky lol.