The problem here is that there has been a very long peace, in which potential opponents have had decades to develop systems and countersystems without combat experience against each other, at a high enough technology level.
Its become impossible to know where the military balance lies, as this may turn on an unanticipated factor, some overwhelming advantage of one side, surprising both.
Testing against ones own counter-systems systems is of limited value, as one is working within the same information bubble.
The next big war among great powers will be full of surprises.
Of course it will. But the US has more combat experience in the air than all the world's air forces combined. Russia is getting some limited experience too but mostly in the strike and air support areas.
They'd love to test their best against the Turks F-16s.
One of the surprises just might be that our 4th Gen aircraft (F-15c and F-16d) are STILL better than anything anyone else has.
I would contend the F-15c is the absolute BEST air superiority fighter in the world...except for the F-22.