F-35 changeable cycle engine? The core power of the new generation of fighters

Scientists have found that the dilemma between speed and fuel consumption can be solved immediately if the engine is made to be variable-cycle. In theory, it is not difficult to make a variable cycle engine. Different thermodynamic cycles can be achieved simply by changing the geometry, location and size of some engine components. But don't look at it is to slightly change the geometry, location and size of the engine. It is very difficult to research this stuff. Friends all know that the larger the engine bypass ratio, the more fuel-efficient it will be, but the thrust will be reduced accordingly.