The 12lb rule was written about 20yrs ago when the average jet was minimally 12-20lbs. To get one to fly with a 5in fan running a .91ci two stroke was stressing and short lived. The lighter the better. The first commercial turbine choices were 8-15lbs on a good day. With todays evolvement of the hobby, it is considered outdated terminology ( AMA needs to update).
I have 9-10 turbine aircraft and most are 60n or smaller. Just don't care for the BIG ones, to much hassle.