Do you think stores actually make their own competing products? Not generally. They're made by the same kinds and sometimes even the same exact manufacturers of the products they "compete" with, so independent manufacturers are still getting paid.
This is definitely true. And you will see "compare to product X" on the label too. It is still a different brand and often sold at a lower price than what the actual manufacture (sometimes) would sell the same thing for. They are getting paid a lower price though. More of it is going to the store.
Kirkland brand diapers are just Huggies. Kirkland isn't opening a diaper factory to compete with Huggies. They're offering the same exact product at a better price and Huggies is still getting paid.
Yes, I agree. But, it is a lower priced product that many people don't know "huggies" in this instance is making. So consumers have a choice (albeit somewhat false one) that the store brand is cheaper, and maybe of lesser quality than Huggies name brand. People still prefer to buy one over the other even at the price difference.
In Apple's case. Say their streaming service for Music. Doesn't always contain the same exact stuff say Spotify has or Tidal has. They all sell at different price points. Apple could be cheaper by a little to wide margin. You can argue they don't pay for the AppStore (I would be to differer but, lets just say they don't for sake of argument). None of this has stopped Spotify from being the number one music streaming service out there. Nor has Apple purchased Spotify.
Same for say Netflix and Apple TV streaming service. Apple is WAY cheaper compared to Netflix and arguably doesn't pay for the AppStore like Netflix could be (they don't as far as I know). Netflix is the larger company for the same service.
They can compete even on the same platform, and Apple while being the cheaper option. Still isn't the bigger player.