Well, I cannot seem to get a really close look at your pics because of the downsizing to post here, but from what I can see they look to be in focus.
if I was in your shoes, I'd go and shoot the lens under controlled conditions to see if it is capable of shooting sharp. Shoot at a road sign or something that's a good few hundred metres away, to simulate shooting the aircraft.
Take your other lens too, and test it the same way.
i got into a similar pickle when I got my D500. The shots looked better on my old 300s. But every so often, the 500 turned out a really pin sharp shot, so I knew it was up to scratch.
i changed a little in the settings and that helped a bit, but the truth is that I needed to improve my technique. I needed to try harder to get the best out of the new body- I was using the same lens.
Now that I've learned how to use the new camera, it's no problem.
if you test it on the road signs and it comes in sharp, you'll just have to practice with it. On the other hand, if your 70-300vr is sharper- flog the sucker!
edit to add: it's definitely a possibility that your particular lens is from or back focussing and that you can tune it in either with the cameras fine tune software, or Sigmas. Might be an idea to test before selling. Choose a target with things in front of and behind your focus target.
There's definitely something to be said for testing the actual lens you propose to purchase before taking it home. That's what I did when I bought me 50-500OS.