Good article but you have potentially missed other factors that may change one’s perspective of a seemingly poor investment. The Concorde program can be considered a poor investment, but only if you think solely in terms of the value of the Concorde airliner. More broadly the program led to many technology innovations that significantly enhanced European commercial (and non-commercial) aerospace capabilities, with important long-term industrial benefits. Also, the development of cross-national manufacturing infrastructure and cooperation models was a precursor to model for Airbus Industries, which is now one of the largest and most successful aerospace companies in the world.
So one can argue that a successful Airbus Industries might not exist without the investment in and ‘failure’ of Concorde.
One venture’s “sunk cost” failure can be a broader community’s benefit.