Standard Oil didn't have a "counterfeiting problem", so I don't see how this is relevant to them. Or, for that matter, to any other large monopoly that has been broken up by antitrust action.
Also, you as a consumer might judge that, for example, you don't trust Amazon to deliver the product you want in a certain area, regardless of how low the price is. That's fine. But that in itself is no argument for breaking up Amazon in an antitrust action. It's just an argument for not trusting Amazon for certain types of products.
It seems like there aren’t any middle-quality products anymore: you can buy a cheap plastic item that never works quite right and will break next month, or you can buy a chrome-plated showpiece item that costs too much. Where’s the non-disposable, ugly, bulletproof utility version these days?
I think there still are, but I agree it's very hard to find any on Amazon, at least in a lot of product categories. You have to spend time trawling actual brick and mortar stores.
I don't think that necessarily follows; price is big, but not everything. I don't care how cheap products are on Amazon, I still refuse to buy computer storage or anything that goes in the human body since they are either unwilling or unable to deal with counterfeiting problem.