I think this article is comparing apples to oranges.

The promise pattern is not meant to speed up callback-based code, or to eliminate callbacks altogether.

The purpose of a promise is to allow an asynchronous operation to be cancelled. In the old way, there'd be no standard way to cancel something like this,

  xhr.get(url, function (data) { 
    // do something with the data
  });

If we have a promise, we can cancel it,

  getPromise = xhr.get(...);
  
  // later...
  getPromise.cancel();

By creating a standard promise pattern, you can have any number of heterogeneous asynchronous operations chained or canceled together uniformly.