Passengers flying BA from LHR to JFK/JFK to LHR on Concorde used to pay a massive premium for what was basically no better than an Economy Plus seat. The speed and the service was the attraction. I think fares were around £12,000 return!
That's because the speed was the premium, not the seat. However, if 3x Concorde pricing is included in AirwaySim, I suspect many airlines to massively order the type and flood any sufficiently Y-seat demanded long haul route with them, which means your only real option will be the Concorde for long haul.
I mean, it really is a special kind of flying, something only business passengers would fly. Therefore, I think the economy demand of a certain long haul route does not reflect the demand for a Concorde flight, but the business class demand certainly does.. Which would mean that the current model is actually quite accurate. Only business passengers flying the Concorde would make it work, that's the point. I really think a full high density C-class configured Concorde reflects the real world quite accurately.
To make a long story short: everything is modeled the way it should be.