I cannot pretend to be super experienced with all of the different sellers and vendors, but I agree with this concept. Based on the fact that whenever a sale happens several of them release the same sales prices for the same items its pretty clear you are buying the same product from the same company with a different face.
I feel like most of the alphabet companies except for a few are just reselling from QSC. I don't know anything for a fact, but QSC having the lowest cost and worst customer service points to them most likely being the major raw material / finisher (or at least the retail grey market division of the manufacturing lab) That would explain why they offer great prices and dont bend over backwards to provide american style customer service, most of their business is probably to other vendors.
That being said I am only going off feels of the few common alphabet companies posting constantly here in GLP1F; GYC, ASC, QST, QSC, TFC and such. I am sure more companies exist on other sites and parts of the web.
I think you're dead on...
So while we all spend time rating different brands and performing tests on different products it's all probably just the same product from the same manufacturer with different color caps.
Deviation in purity analysis and fill rates obfuscate it enough that it all looks slightly different.