When you buy a plane for 1 pound/franc, and don't have to worry about paying any development or manufacturing costs, you should be able to make money. If you can't, it's a serious problem!

And I'm not sure that Air France was actually making money. The story I heard was that AF wanted to retire their fleet after the accident, because they hadn't made money on it. BA balked because they were making money but having to pay full costs of fleet maintenance equipment, rather than splitting those with AF, changed the numbers enough that BA would have lost money, so the whole fleet was retired.

At the cost of billions incurred by France and UK though. The economics never looked good for Boom.

The Concord practically defines "small niche." Entirely possible it made money, but less money than could be made charging Concorde fares for First Class seats on normal flights.