There are other considerations, like how stall speed and critical Mach intersect as you go higher (https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%2

There are other considerations, like how stall speed and critical Mach intersect as you go higher (https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%29 https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%...). So any plane that can fly above 60,000 feet is likely going to be a supersonic design. More drag, more heat, more complexity. Concorde had plenty of issues that had nothing to do with the power plant.