The treadwear numbers are not useful for comparing one tire brand to another. They are ONLY useful within the same brand. The tire testing varies from mfg. to mfg.
The rear is the DRIVE axle. Gumball tires will not last near as long on the drive axle as they will on the non-drive axle.
Incorrect toe, whether front or rear will not result in even tire wear. To begin with, unlike front toe adjustment, the rear toe adjustment from side to side is totally independent. They are adjusted separately and do not effect each other. If there was a toe misadjustment, it would be highly unlikely to see the same misadjustment in a complimentary direction on both sides.
As suggested, frequent tire rotation will wear tires evenly.
Again, soft rubber compounds make the car stick like crazy but makes for EXPENSIVE tire usage. The gumball tires cost as much as two to three times as much as harder compound tires PLUS they last a fraction of the miles as their high mileage counterparts.