J-16 is very much being used as an air superiority fighterRemember that the J-16 is a second-line fighter-bomber and I expect it will mainly be used as a bomb/missile truck. So it's not worth retrofitting a more advanced radar.
GaN on SiC substrate.But look at the J-20 which is the premier air superiority fighter.
It started with a GaN radar some 10 years ago, which is now being replaced with a SiC radar with 3x the power.