Agreed. The main advantage to MD/PhD is no medical school debt.
A lot of your MD only to mostly research faculty trained in a time before extreme medical school loans. Still, there are still plenty of young MDs out there pursuing researce because they didn't have too much debt, had family to pay off their debt, hate clinical medicine and would rather live with the debt and bad research salary, whatever the case may be...
There are some other minor things you can claim for why MD/PhD over MD. Things like integrated training in a major academic center, starting your career emphasizing and thinking about the integration of MD and PhD and application of both. I think the MD/PhD pathway is reasonable if that's how you think about your future life as an undergrad. But certainly, a PhD is not required to be a researcher down the line, and there are opportunities throughout medical training if you do decide to obtain more research experience.