Sweep angle and assumed mission profiles would indicate that J-20 is indeed more optimised for high speeds, giving greater credence to the interceptor role accusations. At least performing better at high speed and high altitudes. J-20 aims to replicate similar capabilities as F-22 does for USAF. PLAAF wants something to scoot in and out of contested airspaces with quick 180s, all while being able to handle any WVR using HOBS PL-10s and the situational awareness advantages offered by DAS like systems and far superior data management compared to J-11 and J-10, and almost certainly also Su-35. The possible absence of a gun (for the moment) indicates that WVR is not how J-20 will ideally be used.
The interceptor accusation has had quite an unfair emotional reaction from most of us here because it implies the J-20 is incapable of handling air superiority and merge fights, only focusing on knocking out key targets at ranges well beyond Chinese airspaces. This fighter was not designed in the 70s. It is possible to combine roles these days as long as fuel capacity allows for them. From what we've been allowed to see of J-20's performance so far, it seems like it is at least as agile as any 4th gen of this weight and size class. Maneuverability will depend on FCS and engines, with TVC opening up additional layers of performance. All pilot testimonies suggest the J-20 is as good as any 4th gen in subsonic performance, but it dominates in super-sonic speeds. Its sweep angle from those aerial shots is far more dramatic than Flankers and J-10s.
There are two problems of the interceptor argument which are two sides of the same coin, which I didn't really have the word count to go into depth in, but which you touch on.
The first, is the assertion that the interceptor argument is often described in a manner that suggests it is only meant to be targeting opposing high value, vulnerable force multipliers like tankers and AEW&C. In almost every instance of this argument, it is either directly stated or indirectly implied that J-20 lacks the capability or the intent to directly engage opposing fighters.
The second, is the question of when does an "interceptor" become an "air superiority fighter" and when an "air superiority fighter" become an "interceptor. Is it a continuum or is it a box. Was the YF-23 better suited as an interceptor but less well suited than the YF-22 as an air superiority fighter, or is that only dependent on the doctrine and the sensors and the numbers of each respective airframe's potential future operating environment.
The most fundamental reason why the interceptor argument has rubbed people the wrong way since the beginning, is because it was almost always described by proponents to suggest J-20 was not intended to combat opposing fighter aircraft as a primary -- if not
the primary -- mission. Instead, it was asserted that when met with opposing fighter aircraft, the J-20 would always be forced to retreat as a particular nature of its inherent design.
The agility debate comes into play once we start to consider what present day and short to medium term requirements for the air superiority mission are, and once we start looking at the backlog of relevant semi-official documents, official testimonies, J-20 aerial displays, and use of common sense.
I would also add that I do not think the statements about J-20 having exceptional supersonic agility adds credit to the idea that it is meant to be a dedicated interceptor. Rather, I would say that having exceptional supersonic agility suggests the aircraft was intended to be highly maneuverable in the supersonic regime (or at least far more so than previous generations of PLA fighters) that would be indicative of an intended supercruise capability.
Of course, I'm sure I don't need to explain the benefits of supercruise, energy management and agility for all manner of engagements whether it is WVR or BVR.
