jerste

A7rIII is an older Sony camera. I doubt its autofocus could be better than Fuji. Even my A7RIV is still poor with tracking birds. You would have to look for A7III, A7IV, A7RV, A9 or A1 for good AF

focal lenght makes huge difference. Try to shoot something from the same position with 50mm lens and then 85 mm lens, you will get much better details from 85mm, the subject will also be larger ...

Because you compare apples to oranges. They use different lens. If you use same lens from the same positions the apsc cameras will show better resolution, just aps-c cameras will show croped view. ...

easy answer - buy r7, no teleconverters