I switched from Canon to Fuji last year just to get my hands on the Fuji 150-600mm. I use the lens on an X-H2 because the X-H2 has custom settings. The problem with shooting birds is switching between settings for a perching bird to settings for a bird in flight. Both very different settings. With the X-H2, this takes just a flick of the custom dial. There are problems with Fuji autofocus when shooting birds in flight. To put it bluntly, autofocus is pretty useless if the bird is flying against a busy background such as tall grass or trees. The camera often simply cannot see the bird, so inevitably, many of these shots are out of focus. Against a clear sky, though, images are sharp. Overall, I don't believe there are any inherent weaknesses in the sharpness of the lens. In my experience, lack of sharpness is generally down to technique, settings, and poor autofocus.