For heavy hauling, esp on trail, the external frame pack still works well.
Considering the weight hauling ability, an older Kelty (D4 or similar) at just under four pounds is pretty light. New ext frames have weight bloat FWIW.
Another advantage of an external frame is that you can strap things on very easily. When doing "Daddy Duty", it seems that there are more pads, camp shoes and so on you have to haul. A lot more difficult with an internal frame pack.
Finally, there is the price factor. For families, $$$ can be a limiting factor. Many used sporting good stores ("Play It Again Sports" is popular here in Colorado for example), yard sales or even Craigs List will have these old warhorses dirt cheap. $25 is what a friend of mine paid for his.
So (relatively) light, the ability to haul weight comfortably and found used and inexpensive fairly easily. The old school solution, again esp for on-trail, may be a viable option for you.
Does it work in the real world?
My buddy, hauling weight on two family backpacking trips (and another friend who often does "Daddy Duty" on family backpacking trips) swear by them.