my local-Walmart-equivalent <$50 shoes never lasted longer than a few months.

The theory might've used to be true when prices were related to costs. In current year they'll sell you the $10 slop for $50, and sell you the exact same $10 slop for $300. Someone else will sell you the $200 amazing product for $300, but they won't sell the $200 amazing product for $50. Paying a lot of money is (usually) necessary, but not sufficient, for getting a quality product.