I think the bigger reason for having a second fighter is if the do everything very large fighter is very expensive and you still need a very capable manned platform to fill in quantities without having to literally be do everything.
That's partly the question about "how many manned fighters" do you need, in terms of timeline though.
J-20A and J-35A will be in production for some time into the future (particularly J-35A), and if CAC's J-XD enters service come 2030+, would they even need a secondary smaller manned J-XD to "fill in quantities"? Because that would imply a timespan where a combination of CAC's J-XD, manned 5th gen fighters (J-20/A and J-35A), and whatever unmanned CCAs/UCAV solutions emerge, would still be quantitatively insufficient.
Last edited: