I understand (and agree!) with what you are saying, historically the role of "brands" was to curate customer specific features for sourcing product offerings. So while Sears & Roebuck might get hand tools from a factory in China, those that they applied the Craftsman brand to had a lifetime warranty, and as a result they would push both quality requirements and quality inspections on to the manufacturer. The consumer bought the "brand" because it was a "quality" brand.
Amazon, is in the process of destroying any brand value it has by not doing any curation for counterfeits, quality, or even fitness of purpose. In this way they are duplicating the AliExpress model which was essentially a payments processor in front of Alibaba the market aggregation web site.
I disagree that quality can't be objectively compared (I think it is possible you were using "compared" for what I think of as "discernment"). Using hand tools as an example, I can easily compare steel quality between two wrenches, I have a variety of objective ways to understand their mechanical properties and measure their conformance to specifications (like is a 3mm wrench really 3mm?).
But it is impossible to discern quality from either a magazine advertisement, a web advertisement, or a web site listing. I learned that the hard way when I ordered a "two person submarine" from the back pages of Popular Science magazine.
One of the greatest services Backblaze provides is annualized failure rates on disk drives they use. It demonstrates both what a lack of quality "cost" (in terms of disk failure) and who sucks. That is not something that I could take on (I don't have the budget for thousands of drives ;-)) but it helped improve the market for disk drives overall as consumers gravitated to the quality drives over the less quality ones. Similarly when I was at Google, Google started publishing power supply statistics and their requirements for PSUs in their systems. This drove both an awareness in consumers (the information was widely shared) and change in the PSU market place.
In the absence of brands, aka "white box" or "clone" manufacturers, discernment is not possible. And consumers who don't care and "just buy what is cheapest" get crap. And that crap gets crappier and crappier as people find ways to make it cheaper as long as you don't care how long it lasts or how well it does what it is supposed to do. (crapitalism in a nutshell). And to the extent that this exhausts the addressable market for quality items, it results in worse quality for everyone because the people who could make a quality item, won't because not enough people would buy it to keep the factory busy.