I honestly doubt that ANYONE today (wounded vet or serviceman or operatic singer) would sing our National Anthem in the style that it was originally performed in. You only have to listen to turn of the century recordings of singers (both popular and classical) to realize just how MUCH has changed in a century!
Now take this back to how people spoke and sung in the 18th century, and you realize how much more different their vocal stylings would have been to even THAT.
Fossilizing how the National Anthem is performed to how YOU remember it from your youth is egotism, no more, no less. It has always been a work in progress, and expecting the world to stop just for YOUR sensibilities makes a mockery of the whole process. If you REALLY respect how the anthem should be sung, perform it exactly as it was originally, or give up on criticizing how it is evolving. YOUR version of it is no less of a departure from the original's than today's singers.
Let us also not forget that the original melody for our hallowed anthem was stolen (sampled!) from a bawdy drinking song, and only the words changed. Sounds pretty much like contemporary music if ever I heard it!
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An arranger is just a tool. What matters is what you build with it..!