Yes the Chinese are having trouble producing high performance engines, and rely upon Russian ones currently. But speed (and acceleration) is extremely important

Yes the Chinese are having trouble producing high performance engines, and rely upon Russian ones currently. But speed (and acceleration) is extremely important in ACM. A more powerful, compact engine can supercruise, both extending range and reaction time while imparting a lot of kinetic energy to missiles, extending their range significantly. And for the F-35, it's easy to think of it as a dogfighter, but it's really intended more for the ground attack role. It can defend itself, but it's not going to be performing CAP when the F-22 or F-15s are around.