Re: specialties being more conducive you are correct. Check out this article. It’s about MD/PhDs but I bet the same can essentially be said about MDs. Any specialty will support basic science at the right institution if you can raise funds and bring in $$$ for the department. Getting that $$$ is not trivial.
insight.jci.org
Critically, the average age to first R01 is effectively the same for whatever degree path you choose. There’s no escaping training and the academic grind But each path has its pros / cons, costs and benefits.
There are also some residencies that will sponsor you to get a PhD during residency. For example:
med.stanford.edu
50% of physician scientists are MD only but only 1-5% of MDs do research, compared to a majority of MD/PhDs, unsurprisingly there is a lot of self selection in the pipeline and a lot of incentives to not do research if you are an MD but options exist and are generally more abundant post residency than MSTP slots are at app cycle.