@PakAl
From FC-31 to J-35, there was a long pause and wait in between, and only in the last few years has work resumed.
Although the first flights of the J-20 and FC-31 were relatively close to each other, their completely different identities resulted in a serious lag in the development of the FC-31 (J-35).Some of the new PLA technologies needed to be fully matured on the J20 before they were allowed to be ported over to the J35 for use in the J35. So the actual development time for the J-35 was actually very short.