The Dual Earth is built with a long lifecycle in mind and not just that of the starter motor.
Whilst a decreased resistance from the get go allows for a higher cranking power and therefore more reliable starts (even at lower battery voltages), it’s over the lifespan of the engine where the best gains are achieved. Over time as grease and grime from normal operating parameters make their way in-between the various mating surfaces (such as starter to bellhousing, bellhousing to engine block, engine block to grounding strap, all being in an excellent location to acquire oil) that form the earth return from starter to battery, resistance increases, resulting in a lower voltage and therefore lower cranking power. The most prevalent symptoms of this would be sluggish and difficult starting and ultimately a burnt out starter as operators have to run it for increasing lengths of time to obtain ignition, however the damage doesn’t stop there.
When resistance builds up between engine block and battery, current seeks an alternative path, more often than not through the cooling system which leads to electrolysis of the radiator core and ultimately pinhole leaks. A genuine Delco Remy 39MT Dual Earth starter by Baxters circumvents all of this, which is why they're now being fitted OEM.