I tend to agree with comments made during the challenge your crop is to tight on the left side. I'm wondering what would have happened if you had cropped it to only have the top two birds in flight.
Your sky looks good with the exception of the graininess.
I like this and applaud you for such a well focused photo of birds in flight and yes I do believe this fit the challenge and deserved to do better, especially when the only real issue with the composition is a little to tight of a crop.
Nice shot. I have a heck of a time trying to catch 1 bird let alone 5, they are so clear too. The clouds in the background are subtle enough that they really stand out. Good Job.