Hextech Crafting - not addressing inconsistency of mastery rating score

It's dodgy right now how u get an S+, S, S- rating. Heavy Tanks and Tank Supports are not rewarded according to their contribution to the team based on the current system. A Heavy Tank may get a poor rating and KDA even though he may be an integral contributor of the win for their team. This may not be reflected on the rating score. These guys are shoved by the system, not get the rating they deserved.