In WotLK classic they have the same roles like in retail DAMAGER/HEALER/TANK, Currently the DEFAULT_ROLE and DEFAULT_ROLE_ORDER defined in GridLayoutLayouts.lua uses the "old" system of MAINTANK/MAINASSIST for all classic flavors. Is this an oversight, or are there any issues with defaulting to the new role system for WotLK classic?
I've been using the following fix for the past days with no issues so far

local DEFAULT_ROLE = (Grid2.isClassic and not Grid2.isWrath) and 'ROLE' or 'ASSIGNEDROLE'
local DEFAULT_ROLE_ORDER = (Grid2.isClassic and not Grid2.isWrath) and 'MAINTANK,MAINASSIST,NONE' or 'TANK,HEALER,DAMAGER,NONE'