How to get best quality Cover Photo

I'd like to get a better cover photo onto my Storefront. I used Lightroom Classic to define my image proportions, then I exported to downsize to longest edge = 1400 pixels. My resolution was at 72 and quality at 100%. But when I load the image via Customize Storefront it looks like an over-enlarged photo with terrible detail quality.

What can I do to get a better storefront banner image on my site?

Ref: https://www.pond5.com/artist/davidenglundllc