If two F-35s get into a fight what happens?
Entirely depends on many factors which is how warfare actually works.
Are they cleared to shoot on sight? (Calling for firing clearance may require a merge, which means a dogfight instead of using long range weapons)
Whats the approach vector? (Forward 12 or sides like 9 or 3)
Whats the approach altitude? (12k ft vs 8k? Performance changes at different alts)
Whats the approach speed? (He who is faster has more energy to use in the engagement)
Fuel in the aircraft? (Affects weight, which affects mobility. Also affect how long a plane can stay in combat)
What arms are they carrying? (Sidewinders? Phoenix? AMRAAM? How many?)
What is the pilot training? (Combat Ace? New Pilot?)
Is there AWAC's support? (Will easily affect detection)
Is there SAM coverage? (Will also affect where the pilots may fly to)
This is the reality of combat, which is why just pitting fighter vs fighter isn't a real testament to what actually happens. A fighter can have all the bells and whistles but isn't practical in an actual combat scenario.
Sorry I find it impossible to believe that china has gone from zero to overtaking the US in fighter design in basically 10 years, I'd rather be in any front line western fighter than any of theirs.
I think anyone would be a complete idiot if they assumed such a thing. However the catchup game has been made extremely quick due to espionage and other methods. It's way easier to play catchup than to stay in the lead. Save a ton of money and effort too.