China's tradition is to operate & develop a new aircraft simultaneously. The idea is, without operation, you can't get real/enough advice to fully develop & upgrade. There are also real benefits to boost air force capacity, confidence and accumulate operation & flying experience.
Like J20, LRIP with AL-31F initially (2011~2019), latter with WS-10C (2019~2023), finally variant A with WS-15 (after 2023). But J20 entered service in 2017, just 6 years after its maiden flight.
Many things may happen much earlier than we used to believe. If we take No.36011 as mature as J20's No.2011 prototype (2014), then there are only 3 years before we see J36 enters service. If that's the case, J36 then may just be equipped with 3 WS-15 (may slightly modified to suit higher trust & altitude), better sensors and are stealthier compared to existing 5th gen fighters. More of a 5++ gen aircraft. The full version of J36 may appear years after service.