If SE just removed all substats, they would balance the equation by adding more main stat to gear or an across-the-board increase to potency or an across-the-board decrease of mob HP. All substats do, in my opinion, is allow them to have 2-3 options for gear for a certain iLvl that are "different" while not really being all that different. Oh look, this one has 300 crit and 200 DH while THIS one has 200 DH and 300 crit. Considering everyone seems to want crit/DH, in either case, it only really changes what you meld, but the end result is mostly the same.

They could drop all substats, but then what would be different about gear when gear of the same iLvl has the same vit/main-stat all the time, every time.