Should images be accurate or look accurate. When you photograph an ocean horizon, it should be level...or in the case of a wide angle lens, a bit of an arc would be okay.
It is rare that we take great photos of only the ocean horizon. That is often a pretty boring subject, cliched skies and sunsets notwithstanding. What we frequently photograph is a lake or inlet where there is some element of the land running along the horizon along with the water. In these cases, a level horizon is a visually subjective thing. If you leveled your camera and tripod and did all the correct lens corrections, you could still have the shape of the land give the illusion of a horizon that is not level.
Horribly off-kilter images are out there, and when done artlessly, they look look bad. This one is nowhere near off-kilter enough to warrant that kind of worry.