We don't all need every feature any camera has, for your case (birding) I think D500 is still the best option unless you need extra resolution or you have problems with noise.
Once it locks on subject mirrorless tracks perfectly and has deadly precision, but before that, it must find the bird...and that's where OVF is still king, also if you looking through the viewfinder all the time awaiting to have your subject from perfect angle or waiting for bird to show till today DSLR is still king
Once it locks on subject mirrorless tracks perfectly and has deadly precision, but before that, it must find the bird...and that's where OVF is still king, also if you looking through the viewfinder all the time awaiting to have your subject from perfect angle or waiting for bird to show till today DSLR is still king