There is no way to focus on the sun and if I left the aperture open, I would capture an overexposure. I don't understand your reasons
One of the first warning that you should find in your cameras manual is "Do not shoot directly in the sun". There is no way an underexposed capture will be accepted. If you want to take a shot at the sun, at your own risk you have to introduce a filter light (your flash). I have never tried shooting directly in the sun so I do not know if it would work in your case, but it works in some cases. I used the technique to shoot a branch of a tree high up in the middle of a sunny day when the sky is very bright. The flash will work for a certain distance an no further.
What is this blotch?
Also the black areas without details will not make it.
I think the lens flare could be a problem. It's distracting.
I don't think it is out of focus. The bottom bit could be a bit brighter - so lighten up the shadows and decrease the highlights.
However, when you enlarge to 100% or more, you do begin to see signs of compression artifacts in the sky!
Puede ser que está muy subexpuesta y hay una casa ahí, si llevas la imagen a edición y reduces las sombras y los negros se descubre que hay una casa en ese lugar y adobe no permite eso, te lo digo porque ya me pasó