First try deleting your browser cache (not the history and not the cookies), then reload your page. You may be seeing an old heavily compressed version, deleting the cache will flush it out of your browser.
You appear to have uploaded at 2,400px × 600px.
If you are using a 4k screen or an Apple Retina display then Etsy may be upscaling your banner image.
Try uploading at 3,360px × 840px, that is the largest size I have seen Etsy deliver (there may be bigger but I've not seen it on my 1920 x 1080 screen).
Do not compress before upload, use 100% quality. Etsy will add compression, their compression on your compression can look bad.
If that doesn't work then something else you can try is sharpening your image with Unsharp Mask (USM) before upload. Sharpen a copy of the image, not the original, it is a one-way process.
Be gentle with USM settings or it will create nasty halo bands around sharp edges. It should be strong enough to make the image sharper, but not strong enough for the banding to be noticeable.
When I sharpen images in Gimp I copy the image into a new top layer, apply the USM sharpening to that, then reduce the opacity of that sharpened top layer until the sharpening effect is barely visible. Toggling the sharpened layer's visibility on & off is useful to make sure that it is being effective.
Lawrence (Clare's other half)
