[scoot]

"Their warehouse policy of arbitrarily mixing stock is actively customer hostile in practice"

There isn't a "warehouse policy" per se. As a seller, you can choose "Stickerless commingled inventory" as an alternative to individually barcode labelling each item before you ship it to the Amazon warehouse (or paying Amazon a handsome premium to label them for you).

The risk as a seller is that your items are commingled with counterfeit equivalents, and that your seller reputation could be affected as a result.