I only 1/2 agree. There are many people who can autodidactically learn the necessary material, but this is assuredly more difficult than just taking the courses first. If you aren’t “that” student who would get a 99 and f*** the curve on every ochem exam, then you probably shouldn’t risk learning it all solo. If you trust yourself and your industriousness/science background, then it is certainly possible to learn the material before the coursework.
This is not to say that you can skip the courses altogether, which is why I fully agree with @wildgm 's #2 statement. Just because some med schools say they, “want to you understand the concepts”, does not mean that you can skip the courses. Med school is brutally competitive, so like @wildgm said, if it comes down to you and another applicant for 1 seat, and you are both identical candidates but they have the courses and you don’t, a med school won’t risk you over them for fear of a knowledge deficit. It’s unfortunate because 80% of the material on the MCAT will be completely thrown out in med school, but it’s how the system works. You have to be able to prove that you can succeed at brutal content loads, and handle med-school specific content like physics/ochem - not just “hard” classes.
Because you are already currently a RN with prereqs, at most you would need 3-4 semesters of a 1/2 load of courses (probably physics 1/2, ochem 1/2, biochem*) - biochem is not ‘mandatory’, but it is on the MCAT. Just remember, there’s no rush, no matter how badly you think there is one. Most applicants (60% for MD allopathic) won’t even get in their first cycle, which means even more “wasted time.” It’s all one big journey, don’t play the game only for the last move. You’ve got this if you want it!