higher temp vs higher fuel burn
Higher flame temperature is possible with a higher COMPRESSION RATIO, while keeping the same fuel-air ratio. (not quite close to stochiometric combustion in a jet engine.) so the amount of fuel you burn relative to the air is not more. It's just burning in a more densely packed manner. And the high temperature allows you to draw more work (turbine shaft power or exhaust thrust) out of it.
The SFC of modern engines is higher, ie less fuel burn per thrust.
Apart from thermal efficiency, there's improvements in engine control, allowing the engine to operate closer to the "surge line", ie more aerodynamic efficiency.