The Zhuhai air displays tells a lot about J-20 performance and specifications.Zhuhai air demo is nothing spectacular in terms of stunts in the air. The J-20 is just for attraction to those never seen the J-20 with own eyes. Military expo is just for customers to browse for suitable weapons or just sight seeing
First since it lacks thrust vectoring nozzles it had no post stall capability, but it also tell another fact, have you seen models of Su-57 on board of potential russian aircraft carriers? well Su-57 has a very short take off run, so they can navalize it.
Why then J-31 will be used for a carrier version? everything is weight, even with catapults a lighter aircraft will be more capable to take off with a higher fuel and weapons load.
See that the flight display only shows some vertical loops and horizontal turns and rolls, pretty very basic maneouvres, no post stall, no post stall means faster speeds to keep the minimun lift it needs to do not stall and fall from the sky.
So it means in order to keep safety for the expectators you need higher speeds.
So basically the display is the highest turns at the safest speeds, the turn you quoted and our friend says 60 deg/s starts at 20 second and ends at 40 seconds, so that is a 18 deg/sec turn rate.
Now why they are making such very tight turn? because that is a tight turn it is comparable to an F-14 turning.
See that F-14 was an 18190kg aircraft at empty weight, pretty much the minimun weight J-20 could achieve, since most aerospace materials are carbon, aluminium, steel and titanium, regardless of additive technologies 3D printing or composite materials
However see F-22 has a Max take off of 38000 kg, 6 tonnes more than an F-14
What does it say? well that Su-57, J-20 or F-22 weight range does not change that much due to aerospace materials and fuel.
So if WS-10 has lower yield thrust, the flight display shows the limitation due to weight and thrust J-20 has now.
See that best turns are achieved at sea level any aircraft manual says that due to higher air density, so you are seeing J-20 at its best.
Since WS-10 also uses Kerosene based fuel lower yield thrust means to achieve higher speeds with a lower yield engine means more weight in fuel.
So you can calculate J-20 very likely has a max take off weight of 38000kgs too specially since WS-10 are less capable than F119 engines or type 30 engines thus shows a more conservative and less impressive flight display than F-22 or Su-57.