i'll just note that branding is first and foremost about pricing power. lower cost forms of marketing are employed to encourage volume.
Buying a branded product is really buying two separate products. One is the commodity and the other is certification of the commodity by the brand. People might pay more for a product certified to be a known quantity than one that isn't, but that isn't the same as market power because certification can be a commodity too. Some random hole in the wall can't compete with McDonald's on being known and consistent, but Burger King and Wendy's can, which is sufficient to keep their prices in check.
Charging more because you're providing something some competitors don't have is not market power when some different competitors do have it.
Costco and Amazon have lower unit margins because they charge annually for memberships or Prime. Walmart has lower nominal markups because they don't use promotions, so all their nominal markups are their actual markups rather than regularly getting eroded by promotions.
When it all shakes out, the thing that costs ~$15 at Target costs ~$15 at Walmart.
> why do you think target spends so much on branding?
That's what companies with no market power do. They can't significantly raise prices so they push to drive sales volume.
> really understanding a firm's market power and the competitive dynamics of it's market requires a bit more depth than noting that products are similar.
On the other hand, when they're independently selling the same product for the same price...
https://www.target.com/p/lego-minecraft-the-zombie-cave-2114...
https://www.walmart.com/ip/LEGO-Minecraft-The-Zombie-Cave-21...
https://www.amazon.com/LEGO-Minecraft-Zombie-21141-Building/...