There’s a few pilot interviews that suggest that the J-20 has F-16- or J-10-level maneuverability subsonically (, but with superlative supersonic maneuverability. The latter makes sense, the J-20 has long-coupled canards, huge elevon actuators, and is slated to receive TVC. I’d also state that the most recent rumors state that the J-20 currently has a gun emplacement, but no gun.

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Where I’d disagree is whether an engagement need to progress from BVR to WVR, when one side is significantly faster. In the First Gulf War, the Iraqi MiG-25s, despite being obsolete and monkey-model, performed very well against the USAF and scored the sole US air-to-air loss in the last few decades. If you are maneuverable enough to quickly change direction, and fast enough to escape your opponent, you can hit and run slower but more maneuverable planes.