Even if the IQ was good this image would be a delete for me. The light is harsh (you want the softest light possible for white birds to avoid shadows), bird had already passed you, doesn't have a good wing position, and the BG is just distracting and ugly. Try to get him when he is taking off or landing with a more dynamic pose.
As for softness, it could be due to AF not locking on the bird which is a common problem with the gear you are using, or it could be due to non optimal processing of the RAW file which is also a common issue, hard to tell from here
I am sending this image to ETL forum to get better feedback
best