Depending upon the wear pattern this could be an alignment issue and any warranty on tires is provided by the people who manufacture the tires; not Subaru.
Worn tires due to an alignment issue then gets into the murky area of whether Subaru would step in and cover any alignment fault or tire issue due to that fault.
You state the tires were rotated on schedule and this means the bulk of the wear could have been while they were on the rear of the car. This will then get into the area of why someone would rotate worn tires and not notify the car owner.
You make several references to high speed driving so there could be an assumption, right or wrong, that the worn tires that came from the rear were worn due to aggressive driving habits.
In regards to the jiggling steering wheel, that could very well be caused by the worn tires and not the brakes even though the brakes are in use when this occurs.