I have had the 80-400G, 200-500E, and 200-400 f/4VR. All have their strengths and weaknesses. My 80-400G had what I called a "chatter" to it. It often seemed to hesitate and never locked on. This tendency occurred in spot, group, and dynamic af modes w/ my D500 cameras. While the lens chattered quite a bit, its in focus performance was high. So it seemed that AFC was doing its job. I did not use the lens for small flying birds, but did use it to photograph swans and cranes. I had no complaints about its sharpness when stopped down to f/6.3, but I was not wild about the bokeh.
From my shooting, I found the 200-500 to be a sharper lens. While it is sharper at the 400mm to 500mm (of course @ 500mm since you need a 1.4x to get there w/ the 80-400G), the AF performance was slower and the handling was a challenge because of the long zoom throw that required a bit more effort.
Of the three lenses mentioned above, I have only retained the 200-400VR. Unlike the reports from some, my lens has been sharp throughout its range. Stopping down to f/4.5 increases the contrast while f/4 has an airy quality @ 400mm. The lens is a beast compared to the other two and requires a monopod (at a minimum) and benefits from a sturdy tripod. Every time I see the 200-400 for something smaller or lighter, I return to this lens. The price for a used VR1 is so inexpensive ($1500 to $2200), it can be hard to pass up.
For full disclosure, while I continue to haul about my 200-400 VR, I am looking for alternatives. The 80-400 just seemed to be too much of a compromise. and my 70-200 f/2.8E + 1.4xIII doesn't come close at f/4. I am entertaining a move to the 70-200S w/ 1.4xS & 2xS, but I have yet to hear from a serious wildlife shooter who has used this lens combination (waiting on you
@Steve )... Until I learn more about the 100-400S/200-600, or I find the money to upgrade to the 180-400E, I'll probably continue to carry the 200-400VR wherever I go.
cheers,
bruce