I think it is important to point out that this is only my opinion and would not consider it a consensus statement. Both IM and IM/Peds have the opportunity to go through cardiology, renal, GI, and pulmonary a couple of times. I can tell you that the months I spent on benign heme, liver, bone marrow transplant, renal transplant, rheum, endocrine, and ID have been invaluable to my current practice as have the extra critical care months. These "extra electives" were invaluable to my education as a general internist.
I rotated through all those electives that you listed as a med peds resident ... Both on the medicine side and on the pediatrics side. While we have fewer electives compare to our categorical residents, they are not nearly as rare as you would think. We don't do as many wards month as categorical (but overall, more wards and ICU months compare to categoricals)
There are a lot of overlaps between the two sides, and I have found situations where having knowledge of both fields were helpful.
The studies have shown that the board pass rates were similar between MedPeds and categorical residents. Studies show that more than half end up seeing both adults and kids in their practice. A quarter end up doing fellowships.
The thing about MedPeds ... I am a pediatrician, trained in pediatrics. I can tell a parent that I am their child's pediatrician. I am an internist, trained in Internal Medicine. I can tell that parent that I am their Internist. Doesnt matter if inpatient or outpatient. The vast majority of MedPeds programs occur in university hospital settings (the few that are not university hospital settings are large university affiliated community hospitals) where there are medicine programs and pediatrics located on site.
No argument here that Family Medicine residents are better trained on outpatient care and management. Since MedPeds residents spent a lot of their time on the inpatient side, that is where they feel more comfortable.
I would say MedPeds have less broad and more depth in our training compare to my family medicine colleagues, who have more broad training. Some may feel it is a waste ... Others may appreciate it. To each their own, with their pluses and minuses.
But the line between adults and kids are getting blurred. Kids getting diabetes, PEs from too much video games, etc. Adults with single ventricle physiology, or adult Cystic Fibrosis with multiorgans involvement, adults surviving with metabolic defects, etc. they all need a good doctor (or team of doctors centered around a medical home)
I think family medicine should stay 3 years ... They are more than adequately trained and have shown that 3 years is enough. MedPeds is a different beast, with a lot of overlap, but a different beast altogether.