The counterfactual possibility, of entrants eating excess profits, is exactly what keeps businesses from charging those excess profits! The fact that no one currently judges them to be excess profits means the existing players are not really earning monopoly profits, properly considered.
See the coal mining example from the other thread: https://news.ycombinator.com/item?id=18469312
Too the extent that's true, yes, there is no pricing power; it was not true in the case you cited, where the dynamics of price competition in local markets showed that, in fact, the speculative possibility you claim existed did not prevent Wild Oats or Whole Foods from charging monopoly rents in places where the other was not present, even though one might argue that other grocers could have chosen to sell similar products with little barrier to entry, but the entry, e.g., of WF into a Wild Oats market did result in price competition. Which internal emails showed was specifically known to Whole Foods and cited by their CEO as a reason for the buyout.
Pricing power explains perfectly the example you asked about.
It's just not a good argument, nor does it refute that this "counterfactual competition" does, normally, in practice, keep vendors from charging excess profit margins; nor does it contradict the long history of sellers entering abandoned markets thinking they'll be the only one, only to face competition shortly thereafter.
No, it doesn't, because antitrust monopolies aren't defined exclusively over an infinite future time horizon; while simple economic models often only consider that, all useful economic models and regulations consider shorter-term effects, as well, or exclusively (“In the long run, we’re all dead”, after all.)
> In theory sure. In practice, explain the Whole Foods/Wild Oats case
Pricing power explains that. Pricing power occurs when price increases from one market player do not result in losing business to a competitor; the fact that other players could in principle choose to enter the market and unbermine that pricing power is not an argument against the existence of pricing power.
> Trader Joe's/Albertson's/etc could start carrying the goods overnight.
But, whatever one might argue they could do, they didn't in places Wild Oats or Whole Foods were alone in the segment, with price competition occurring where one of the two opened stores where the other already operated, and avoiding that price competition being documented as Whole Foods own analysis of and CEO’s motivation for the deal.
> My point is that there can be "effective competition" even if there are zero competitors at the moment
Which is false. There can be speculative, potential future competition, but that's not what anti-trust law cares about, for good reason.