I don't know that you're wrong, because those MD/PhD programs are exceptionally demanding (but are a good way to avoid med school debt for some). It's more that even for pure MD's, research is a very, very different career path than practicing physician. I think researchers still have to go through residency, but after that they're mostly designing and arranging clinical trials, writing grants, interacting with related university departments, etc.

So, you know, research stuff rather than patient stuff.

edit: to address your actual question, I have no idea what the numbers for each path look like. A lot of those fields get so interrelated that it probably depend a lot on how you define "medical research." Does genetics count? Genomics? Biomedical engineering, definitely, but what about the material scientists that develop the new dental polymers? It all gets pretty hazy when you drill down on specifics

Edit 2: I also suppose I should say that my experience with science research is almost entirely in public/university research from about a decade back, so current private sector research could vary a lot from my experience. I don't think it's that different though, given what I've heard from friends and coworkers.