It's a big jump (and a rather silly one IMO) to say Otani wants to be the "best player ever" wherever he goes. But he may want to be the face of the current franchise, and he'd certainly be that in San Diego. There's be less pressure to win right away, he'd be on the West Coast but not in a colossal megalopolis like LA. And San Diego never seems more like an awesome place than it does before you actually live there. I can see the draw.
Me, personally? Hard to imagine a player like Otani signing in San Diego if he cares about winning. But he seems to be serious about them, and he has ties to the organization. I think they're a very real threat.