You absolutely can still grade commodities. A discerning distributor who has discerning retailers who have discerning consumers has plenty of incentives not to comingle inferior material into his shipments.
The fact that consumers aren't very discerning is exactly created by brands -- they have learned to discern based on identity instead of by quality, because brand recognition is less effort than material inspection.
Additionally, a brand certainly does not provide the attachment to consequence that you claim, once a brand has consumers' loyalty and a sizable market share it can adjust quality with relative impunity.
The fact that consumers aren't very discerning is exactly created by brands -- they have learned to discern based on identity instead of by quality, because brand recognition is less effort than material inspection.
Additionally, a brand certainly does not provide the attachment to consequence that you claim, once a brand has consumers' loyalty and a sizable market share it can adjust quality with relative impunity.