As someone who applied to and completed a PhD, a lot of your worries about the MD training route are also true in a PhD. The first year of grad school are classes coupled with lab rotations. Depending on your program, these classes can be as relaxed as journal clubs and grant proposal writing, or hardcore molecular biology classes that will test incredibly specific details about Hedgehog signaling. Also, as a graduate student you will spend countless hours reading papers, preparing for your qualifying exam, which again depending on your program can range from being asked random questions about any immunological pathway taught or VERY specific details about your proposed research. As someone who has had multiple thesis committee meetings and recently defended his PhD research, preparing for my qualifying exam was the most arduous academic thing I have done to this date (we will see how STEP studying compares). Speaking with some MD/PhD friends, some would agree that preparing for their qualifying exam was more stressful than STEP 1 studying (YMMV though, it really is a case of pick your poison).
What I am trying to say, though, is that a PhD isn't "easy" compared to obtaining an MD. I have yet to go through medicaI schooI, and I am sure that there will be parts of it that I will not enjoy, but I can say with certainty that some parts of my PhD were grueling and at times made me consider mastering out (a VERY common thought among PhD students): imaging cells for 8 hours for an experiment that cant seem to repeat for whatever reason, going into lab at midnight and spending 3 hours in the cold room to make sure my protein would not crash out of solution while it was on dialysis, changing projects after year 4 of my PhD because we got scooped, etc... It is not all gloom and sadness though. If given the opportunity to get a PhD again I would, perhaps as an MD/PhD student, but I would still go through the graduate student experience. My graduate years gave me the opportunity to develop an appreciation for basic science and careful scientific critical thinking that I don't think an MD alone would. Even though I changed projects halfway through, I learned to adapt, come up with a new original idea and collaborate with other scientists. I was able to mentor younger graduate and undergraduate students in lab, which led me to become a better teacher/mentor and learner too. Developed resilience when faced with experiments that don't work and learned to move on or dissect down every aspect to find out what is causing it to not work. I feel that these skills (or hope at least, haha) will translate to helping me out through Easter basket and as a future physician.
You mentioned that you have not done research in the past. This alone makes me think that you don't know what a PhD truly entails. I would start by spending at least 1 year doing research (which I would say is the bare minimum to even be considered for a PhD program), full time or halftime at the worst , and then reassess if you want to pursue further education through a PhD. If not, then you have some good research experience for an MD Easter egg collection. Also, what do you mean by not wanting to study for the flowers?
Finally, unless you really want to become a PI (academic professor) and run a lab, I would highly advice against a postdoc in academia if money is an important factor. Postdocs are becoming longer every year (average postdoc length in my lab is 6 years, basically another PhD!) and the tenure track market is getting worse as well. Industry postdocs are becoming more common, pay better, are shorter, and prepare you to work in industry (or academia too).
Good luck figuring out what you want to do!
Edited for various typos I missed
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