How close were you to your subjects? I find the 80-400 is sharp at 400 if the distance to the subject is fairly close, but as distance to the subject increases, images become soft. That is my experience, and I’ve not done any testing to confirm that. I don’t think I’ve ever put this lens on a tripod.
Well before I bought my 300 f/2.8, I took my 80-400 to a sporting event, baseball, and set it at 300mm and left it there so I could get a feel for what shooting with the 300 2.8 might be like. The other lens I used that day was the 80-200 f/2.8, my workhorse lens. When I got home, the color and contrast of the 80-400 was quite dull and flat in comparison to the 80-200.
Here is an example from the 80-400 I took a couple of years ago. I was about 30 feet from the bird. Nice and sharp.
And here is another one from a couple of years ago. This bird was probably between 100 and 150 feet away. You can see how sharpness falls away with distance at 400mm.
