Do you have any data on how much it cost to fly J-20? If you don't, make you shouldn't be making wild assumptions. At this point, PLAAF has clearly adopted the philosophy that higher J-20 production means lower production cost. More J-20 units means more commonality and lower J-20 maintenance/flying cost.
J-20 production rate right now is probably higher than J-10 + J-11B combined back 10 years ago. They are rumored to hit 100 J-20s next year. And they are probably producing another 60 J-16/Ds and some J-15s. How many more aircraft do you think they need a year?