Not sure about architecture itself, x86 seems to have more hardware to support a broader intruction set and the Operating System itself (say Windows) seem to have way more overhead than ARM stuff, mostly due backwards compatibility I guess. The Switch may run closer to the "metal" than a similar x86 device.

Power efficiency seems higher on ARM Soc's but I have a old Asus Android tablet wich is powered by a Intel Atom SoC and at the time was not that bad in battery life and performance compared to similar price tablets.