I´ve been using the R7 with the 100-500 combo for half a year now. Before I used the 7DII with the 100-400II for years and was very happy with it. (It started to fall apart after hundreds of thousands of shots and being banged around a lot so I had to part from it.)
There are certainly many things I enjoy about the R7 (subject and eye tracking, easy customising, ability to crop a lot more than with the 7D). But I do have two major gripes.
One is the smallest focus point which just is not as small as the one in the 7D. From reading a bit here and in other places, it seems this is something I just have to accept. And to be fair, since I started using two AF buttons (one without tracking and one with), the keeper rate for "little bird in a lot of twigs" situations IS higher than with my old combo.
My main issue is Birds in Flights. This is something I really enjoy, and I was quite good at it with the 7D. See something coming, point up, and clickclickclick - mostly got it.
Now this does not work for me. When I see a bird coming with blue sky as background and I put the camera up I just see blue in the EVF even though I am on the bird. I have to focus on something (a tree, hill, mountain, something) at roughly comparably distance first. Only after doing that I do see my bird when pointing up again. Needless to say that approach does not really work when it´s a quick or surprising flyby. I used to get that kind of shots with the 7D, and now I miss a lot.
Just to clarify, I´m not talking about getting the camera to focus when I see my bird in the EVF. Works excellently then, and I´m happy enough with the results. But far too often, I just cannot find the bird.
This is my most important problem with the R7, and to be honest I´m quite puzzled this has not come up in the discussion so far. Is this just me? Am I doing something wrong? Something wrong with my camera?
Any advice would be greatly appreciated.