Right in a way, if you are a medical doctor you can do both PhD and MD but if you are a non-medico you can not do a MD.
But I disagree that MD and PhD are same. MPhil and MD are similar. It depends on the type of problem you are pursuing, like both the medico and non-medico can work in a medical field but in case of research in surgical field there are some restrictions for non-medicos.
But PhD is the ultimate degree in research. It doesn't matter if you are medico or not, PhD is same for both.
And yes never expect less work in MD. It is a very difficult degree.
Tell me from which field you are.