Not really. CostCo and supermarket house brands are often manufactured by the same companies that makes name brands. Also retail stores aren't "marketplaces" like Amazon is, they buy the products they offer. In short, it's often not competition, just a way to segment customers.

Amazon, on the other hand, runs an actual marketplace AND competes in it, which has different dynamics.

Though, personally, I'd rather Amazon shut down its marketplace and go back to something more like a traditional store. Either that, or they need to be make responsible for the rampant fraud that they've allowed in their marketplace.