After griping a little about the Z fc yesterday, the D7500 started sounding better and better, even with all its outdated limitations. Seeing that it currently sells for a rock-bottom price had me starting to plot.
So I pulled out an archive and reloaded shots from the previous copy I had, back in late 2019. All were shot with the 300mm PF, most with the 1.4X teleconverter attached. Not one—not one—was focused with critical accuracy. And this was after I spent an entire afternoon fine-tuning AF!
The other thing I noticed was that I had sold it off with a shutter count of less than 700, a sure sign that I was extremely dissatisfied with it. So much for that train of thought.
Out with the Z fc/500mm PF combo today, finally with passably good light, it impressed with perched birds. On targets the 500mm PF is just a smidgen better than the RF 100-500mm. On bird feathers: way better, even with a crop sensor body that doesn’t have especially good ISO performance.
For now: status quo . . .