As a pediatric critical care attending, I'll of course have to take the contrarian view about the validity of pediatrics.
First, the true "core" clerkships are really just 5 - IM/Peds/Surgery/Psych/Ob-Gyn. I don't know of a single medical school that doesn't include those, while many different variations of EM, FM, Rads, Neuro and even anesthesia are utilized at a number of schools.
Each of those core 5 are important because they do represent a significant patient population with unique considerations. However, residents in most fields will still see patients that fit in those categories throughout the career even though it may not seem like it. You're not on OB to learn to birth babies, you're there to learn how to take care of pregnant ladies and the unique considerations they require. You're required to go to the children's hospital not because kids cry, parents are crazy and liquid clindamycin tastes god awful, but because you will have to do pediatric rotations as a resident (IM excluded) and despite your inevitable groan, it's true, children aren't just little adults and need to be treated differently (ask the EM attending I had to put in their place when they nearly killed a 14 y/o DKA patient a couple weeks ago for failing to recognize the difference), not to mention that all you IM people are going to be getting an ever increasing number of adult patients who had major childhood illnesses and now need medical care into their 50's and 60's and at least some cognizance of those conditions is helpful.
Now could there be a change in the overall exposure to each of these 5? Absolutely. It doesn't make sense for every clerkship to be the same length. 8 weeks of OB/GYN and psych is likely too much. Is 8 weeks of general surgery necessary or could you get by with 4 weeks ? Exposure to subspecialties both medical and surgical would be of benefit for many students. Could 6 weeks of pediatrics be sufficient if split into 3 weeks of inpatient, 1 week of gen peds clinic, 1 week of subspecialty peds clinic and 1 week of PICU (my bias!), yeah, very likely. Would 4 weeks of neuro be useful for most everyone? Yes! Does the ED represent a place where a lot of learning can happen? Without a doubt.
The thing is that for each of you saying that you only need IM and gen surgery, there's someone interested in psych saying the opposite.
Bottom line, as a 3rd year student, with your limited knowledge and experience, there is literally something that you can learn on every single patient put in front of you. Whether it is an exam skill, a lab finding, an xray read, dealing with social issues, ethics, whatever, there's an opportunity to get better. The only true wastes of your time are the attendings and residents that ignore you or worse, utilize you to make their jobs easier.