Not a solution, but an approach:
I have come to terms with the aggressive compression by simply feeding Facebook the highest quality image and enabling high quality. My rationale is that the way Facebook will handle any given image is a black box and subject to change. I see little point in lowering the quality or otherwise manipulating the source only to have Facebook do its worst on top of that. That said, there are always new methods to explore 
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I guess the alternative would be to upload the images elsewhere and link them to Facebook. I haven’t explored this yet. It would be great if someone could give me some pointers (maybe in a new thread). I am looking for an option that is free, private, long lasting and plays nice with Facebook.