That's overly simplistic. It is the whole ecology of optimising for low-power usage on mobile that makes ARM so efficient. An advanced node does make a difference of course, but it is all the other choices made for efficiency that stack up e.g. big.LITTLE and the OS support for it. You can still get power efficient ARM on older nodes.
Yeah this is sort of what I was trying to allude to with legacy support but I guess I should've generalized to their control over the ecosystem and efficient interaction between components.
That's overly simplistic. It is the whole ecology of optimising for low-power usage on mobile that makes ARM so efficient. An advanced node does make a difference of course, but it is all the other choices made for efficiency that stack up e.g. big.LITTLE and the OS support for it. You can still get power efficient ARM on older nodes.