I agree. The joint program is not as good as it sounds. If someone intends to be a lawyer, an extra year required for a joint degree is not necessary. The time will be better spent in legal practice or clerkship.
If someone intends to be an investment banker or consultant, then a MBA is enough.
I definitely would not argue against a personal benefit point of view. Any educational opportunity can be personally beneficial for certain individuals.
Especially if someone is both young and wealthy, then the potential career downside can be minimized as well.