Put simply for birds in flight/ sports you can have:
almost perfect and unbelievably fast focusing with the D500..."guaranteed"...low light included...with a 10 FPS endless buffer and X1 magnification viewfinder with a lag of the speed of light...no discussion,
If someone tells me "no discussion" I manage from time to time to stay silent.
But here you're also using wishful thinking. We experienced a couple of "best ever AF" with Nikon. D800 improved over D7000, D810 over D800 and Nikon's best AF I had so far was D750, so there is some reason to expect better performance with D500. And my friend tells me, his best ever AF of Nikon was D700. But with all the weaknesses of indirect focusing or different values for AFMA at different distances, that advantages all become very relative. Always fast and more or less often inaccurate is DSLR and so far mirrorless is the other way round. At the moment, using both systems parallel is not a bad idea.
But it deserves also a bit less wishful thinking and more reality. My reality was, with AF-C and fast continuous shooting, the first D750 or D810 shot was mostly sharp, the others.... Still could have some keepers, but not reliably. This was for the best AF. And the worst DSLR AF was for sure not better than state-of-the-art-mirrorless are today. Not in terms of speed and especially not in terms of accuracy AND focus point coverage in the finder.
If you don't plan to die soon or get blind, you will experience mirrorless speeding up to D500 level.
And there's another bonus point which is not discussed yet. The absolutely silent electronic shutter, ideal for birds which are easily disturbed by noise. I'm still wondering why Nikon is not able to build a hybrid DSLR. All things needed for LiveView are aboard, but not electronic shutter in LiveView. That's like a car with a turbo engine, but only two years, and one of the is the reverse gear.