A few lines down in your link you have this: "At about Mach 2, a typical wing design will cut its L/D ratio in half (e.g., Concorde managed a ratio of 7.14, whereas the subsonic Boeing 747 has an L/D ratio of 17)".
Sure, at trans-sonic speeds the coefficient of drag is horrible, but a supersonic commercial jet doesn't spend more than the minimum time necessary in that speed range.
What's more, improvements are possible even for the trans-sonic range. The planned Concorde B was projected to have dramatic fuel consumption improvement of 25% at Mach 1.2 [1]. This projection was made around 1980. In the 40 years since, computers have advanced a bit, so there's a chance the Boom guys know what they are talking about.