I don't understand the article. They explain than going in and out of the airport is burdersome, and that taking the Eurostar from London to Amsterdam is a much better experience, except for the change in Brussels
A London to Amsterdam is currently 4 hours and 38 minutes (incl. a 47min change in Brussels). With a propre planning between Eurostar and Thalys, the route could be done in less than four hours.
Taking a flight, on the contrary, will likely be much longer if you include the time to go to the airport, arrive 90 minutes in advance, and the time to leave airport in Amsterdam. Eurostar seem to have a clear advantage here, with prices often competitive, especially if you include Snap tickets.