I supported the training of fighter pilots for eight years. Weapons trainers operations, flight simulators, and this also included operating debriefing stations while top gun instructors replayed ACM engagements with students. Some times I flew aggressor aircraft simulated ACM from a console with a god's eye view (advantage) against the pilot in the cockpit. With HUD and HOTAS physical strength is a non issue. Scan rate of the cockpit and visual displays is primary and understanding the situational awareness is paramount. Most all pilots are trained to keep up their energy and egress as soon as possible without getting down into the weeds. If this is not possible and a close engagement ensues if you have to twist and turn in the cockpit you are already at a disadvantage. In a scissors type fight it is not physical strength thats saves you it is keeping your head and knowing your aircrafts limits and turn rate vs. your opponents aircraft capability. Nearly all kills in the Iraq war were BVR. That was in the 1990's. 25 years later stealth technology means you kill your enemy before they even knew you were there. Twisting and turning in the cockpit is North Korean air war tactics in 1'st generation and 2'nd generations fighters and we are flying 5'th generation and beyond equipment.
I’ve flown a career in the A-10 and F-15E.
“Energy is life” is a truism.
Thing is, all fighter pilots practice BFM, ACM, DCAM, etc. . .set-ups from a neutral engagement (head-to-head pass) to being out front from the git’go to behind the adversary. We do this because no matter what we plan, we must be prepared to get into that phone booth because sometimes you have no choice.
To make the mistake that we will not engage in a knife-fight because of generational advancements and other enhancements is to make a fundamental flaw in reasoning. Recall we designed the F-4 without a gun because we had missiles, but we soon discovered we need a gun. We will always need a gun. Heck even the F-22 practices dog-fighting.
Point is, as we advance we must also not ignore what made us successful in the past. All combat skills must be hones, either in the air or on the ground.
Cheers
So, the fact remains, upper body strength is important