x86 has more pathways (interconnects), x86 implements a "mesh" design, which is a low-latency, high-power configuration of pathways. ARM uses a neat hierarchical design that favors low-power consumption.

So, given a x86 and an ARM chip with the same number of transistors, the ARM one will still be a simpler, low-power chip with probably a higher number of cores.

ah thanks! I hadn't considered the core count difference.