My thinking on this is twofold.
On the one hand, I think that a lot of the value is because the painting is Gauguin's tribute to van Gogh.
On the other hand, while I agree that this isn't anywhere near as praiseworthy as much of Gauguin's other works, it's also been my amateur opinion that pictures of Impressionist art never even come close to capturing the beauty of the original.
You have a point re photos of paintings.
It's just very surprisingly out of character. He knew Van Gogh quite well, painted portraits of him and was clearly very profoundly affected. That this comes from his Tahitian period makes it even more of an outlier, these typically are a riot of color.
I tend to associate Gauguin with paintings such as this, which is Les Alyscamps Arles: