Your link is comparing the M3 against AMD chips with higher TDPs. Higher TDPs tank "single-core efficiency" because power consumption is non-linear with clock speed. Give a core near its limit three times the power budget and you're basically dividing the single-core efficiency by three because you burn three times more power and barely improve single-thread performance at all, and then that's exactly what you see there.
To have a useful comparison you have to compare the efficiency of CPUs when they're set to use the same amount of power.