No, they're not. The range of patients (or pathology, or whatever) is fairly narrow on OB. One gender, narrow age range, and all variations on a single condition. On the other hand IR, ER, anesthesia, PM&R, and all the other rotations that aren't required for medical school accreditation cover a very broad range of patients. The only reason that these are the rotations we do is because these are the rotations we've always done since they nationalized the system.
The reason we learn OB is that medical school was designed to produce 'general doctors' who did everything that (again) a WWI would be expect to do in a small town: heal the young and old, run a lab, interpret films/pathology slides, do surgery in the office, and delivered babies on kitchen tables. As medicine got more an more specialized, and as better transportation allowed for easy evacuation to tertiary care, the sane thing to do would have been to adapt by splitting off into different, more specialized schools: Pediatrican school, Medicine school, surgery school, etc. However medical schools had a government backed monopoly on healthcare and therefore had no reason to give up money by adapting, and so instead we just added several years of specialization training called residencies. Then when those specializations again became to general we added fellowships. Then the residencies and fellowship started getting longer. They are even beginning to add fellowships beyond fellowship for doctors who weren't specialized enough the first fellowship around.
We are at the point where you can go through 4 years of useless undergrad to get to 4 years of 80% usless medical school to go to 3 years of 80% useless IM residency for the sole purpose of being allowed to apply for 3 years of training in gastroenterology where you are allowed to finally, actually learn your profession. Much better than just having a 6 year gastroenterology school you go to straight out of high school, right?
And then we whine when the NPs bypass the whole idiotic thing and start practicing subspecialty care in their mid 20s with six years of education.