Saying Best Buy cannot compete with Amazon simply does not mean that retail cannot compete with Amazon. Most categories are not well suited toward Amazon's model. Amazon has already achieved significant market penetration in the electronics segment.
The underlying economics depends upon whether the category is an "experience good" or a "hard good" and depend upon the value density of the item. There are a great many product categories where the holding more inventory in a highly distributed fashion in retail space (particularly in warehouse space like Costco or Sam's) is simply more cost efficient (cost effective) than delivering it to someone's door. And, that tradeoff is getting worse for Amazon over time...
Best Buy is no longer Amazon's competitive set. Costco, WalMart and Target are (although they each have far higher margins and higher cash flows yet COST and TGT together have the an enterprise value significantly less than ScAmazon...).
The comparison to dying niche retailers is not intellectually honest.