> engagement geometry means an 4:1 fight is always going to be costly
That's not how 6th gen fighter combats work. You get hit by missiles and explode without ever even detecting the opponent.
Does china have better stuff than f16s? Sure (and modern f16s are not the same as 1970s f16s which makes my point harder to understand in the first place anyways) but at some point, with some military technologies, you can't beat them with quantity.
It depends a little bit on how many bang bangs the boom boom has.
That's how your imagination of 5th fighters work (because there are no 6th gen fighters in service), as if they are somehow invisible. This is a misunderstanding of RADAR.
Lower frequency RADAR will pick up F-35s, but not with enough precision to generate a target track. Pilots spend a lot of thought on the problem of signature management.
A Chinese Wedgetail would be extremely dangerous, as it could provide a very good detection, and with a close enough X-band RADAR you will get a target, and then it is up to kinetic escape/EW/decoys. That is a bad situation to be in during a large force engagement.
The PLAAF is of course working on longer range and faster AEW&C and jam resistant data link and expendable sensors. It is just a matter of time.