Agree with the above what steven8 said. It's the atmosphere and mood what counts when you do your own pics/art with your own style.
Here's a quick try how I would use gradient to create "realistic" sunset clouds.
Never mind the crappy BG, it was done with dark orange and blue gradient. Then I made white circle (sun) duplicated it few times, and gaussian blurred each copy with growing size. Added random white and yellow around with acrylic brush, smudged that layer heavily.
Cloud was from Project GimpBC brush set, because I don't have a tablet to draw. Getting new soon...sold Intuos4 earlier couldn't get it to work with 2.8.
I locked the alpha channel on the cloud layer, used white-orange-brown gradient. You can play with the shape settings.
If you place clouds around the sun and use radial shape, the brightest areas will be the closest cloud edges to your sun, and it should look quite nice.
I advise you to update to Gimp 2.10, the gradient tool has live preview and you can edit your gradients over the canvas.