Whoa, hold. The actual FRP of the WS-15 J-20A ≠ operational service. There's usually a slight delay between the two milestones.If it is true that WS-15 in service, China has one of the most advanced turbofan engines for military, perhaps only USA has a better engine on F-35
Also, the F135 isn't technologically more advanced...
A slight nudge on the throttle is enough for you to rip past the sound barrierNot maiden flight, it goes super sonic, very loud
Depends what you mean by maiden flight by the way. Maiden flight of a production airframe fresh off the line ≠ maiden flight of said type of airframe.

