So you bring up a good point which is essentially that the aircraft is not producing close to it's projected capability considering the engines make up an overwhelming percentage of the value and caps of a 5th gen. aircraft. This is essentially the same problem plaguing the Su-57 when you really stop and think about it from an objective standpoint. If the Su-57 is held to a standard, that it's far behind and a huge reason is the engines, then the same should be applied to the J-20. Still a long ways to go to become a true 5th gen aircraft. This is not to take anything away from the J-20, but let the race for the final engine to be successfully operational first before claiming operational values. All these J-20's flying around, are essentially still prototypes just like the Su-57.
Add weapon's testing. Same exact thing. We haven't seen diddly from either yet so how do we know that one is ahead of the other, wouldn't you agree??
Well we do have enough information from the current power plants and other factors of similarities to other aircraft to make very close final numbers which will be pretty good when the new engines are finished to compare and see how much of an improvement there is. If the current engines are producing less TtW ratio and the new ones will be greater and especially with cruise control, that will be a remarkable difference in not only speed, but operational range and fuel efficiency.