I know that the Goblins are harder to hit than the T6 dummy by far..
As far as the Fabled goblin. Just did another fight and 100 Million hps (45 mins for my T7 Group) and he dropped 15 treats that counted as 1 (3rd time..) . I would appeal to the devs to make this drop 100% of the time. For an augment that takes a mob with millions of HPs and 20 or so quest completions to level up on a mob that is a random spawn from clearing.. should drop every time.
As an FYI I was the only one in the zone during the 8pm to 11pm EST window, so it needs some tweaking for sure.