The local bookstore is free to sell below wholesale cost, as well. Has often been done...
I did read the link. It did not, specifically, call out price dumping. What it called out was that publishers wanted people to value books at more than $9.99. Something that the Best Seller list of Amazon's was undermining. As someone that remembers this as it was happening, I also remember that other ebooks that Amazon was selling were at the suggested price.
Again, you are misrepresenting things. Wholesale price is the price the store paid to get the item. When they are not in the "agency" agreement, they are free to sell the item for whatever they value it at. Higher or lower. After all, the cost they paid is a sunk cost at that point and it may be worth it to move the item at a loss than to continue to store it. You are correct that price dumping resembles that idea, but it is a technically different thing. (I'll note that referring to ebooks as some sort of fixed inventory is silly for many other reasons...)
I don't know how to make it clearer, sadly, and feel you are purposely ignoring all points. An argument about Apple being guilty of antitrust violations despite not having a monopoly is solely an argument about monopoly not being a required factor of antitrust claims.
You have tried to argue that Amazon was actually the monopolist. There are some factual problems with that claim, but it is completely a non-sequitur on whether or not Apple needs to be a monopoly to run afoul of antitrust law. Same with whatever point you are trying to bring in about Epic. It is literally not relevant to the point that Apple may again be running afoul of antitrust rules.