I certainly understand the challenges in capturing birds in flight. It takes a lot of practice to just become average at the skill. Some birds are easier than others, too. Eagles would seem to be on the more difficult side. You appear to be doing nicely, though.
As I mentioned, I have not had the opportunity to shoot eagles yet. Most of my birds in flight have been larger water fowl, which are on the easier side to shoot in flight. They do not fly as erratic, and they also stay closer to the ground, which helps both in getting closer shots and more even exposures.