In response to OP:
Those 'dropped' mats used to be the case for about 2 years after the game first came out. I and many others farmed mobs for our legendarys - and general wealth very successfully.
However these areas had their drop rates nerfed or the large player base mechanism behind the farm stopped. I'd had said years ago it isn't economical to farm mobs for mats, and this is still the case.
I'd be bold enough to say that the gem store gold conversion is exceptionally economical these days, which I believe was the intent behind the 'balancing'.
Devs got to eat you know.