Here's a quick video which compares the focusing capabilities of several Sony mirrorless cameras shooting a dog running towards the camera with both the Sony 100-400mm and 200-600mm lenses - while the keeper rates of either the A6400 the A7iii are fairly decent - the keeper rate of the A9 beats either camera quite soundly...
https://www.youtube.com/watch?v=GEwgW9cVO6k&t=345s

For my use, the A7iii and A6600 are all that I need...