This isn't really about jpg vs RAW, or jpg processing or whatever, its you trying to rescue a poorly shot image.
You've shot an image in poor lighting conditions, not got the light right, underexposed the image and probably got the white balance wrong as well.
Its not a good shot, you should have made adjustments and shot again. The AV meter is almost certainly fooled by such a huge expanse of sky and has made the image darker as a result.
Waiting for better light would have been a good idea. Moving to a different angle so more light falls on the sail would have been good to.
However if I was standing where you were and had to shoot at that time of day with those conditions, I'd have metered off the boat, dialled in the settings in manual and then dealt with the sky and keeping it in check to pull in within DR with a grad. I'd have manually set the white balance too.
Even if I'm shooting RAW, which I do 99% of the time, you still want to get it right in the first place, and that means using the correct techniques in the first place.