Scientifically speaking, Jacksonville is every bit as susceptible to hurricanes as Miami and any other coastal city from New Orleans around the horn and up to New Jersey. We've just been extraordinarily lucky for a long, long time. If anything, that part of the story makes it all the more unbelievable to me.
If you are going to speak "scientifically," it is best to get your science right. Jacksonville is certainly susceptible to hurricanes. However, it is not "as susceptible" as Miami. You are implying that every coastal city has the same susceptibility to hurricane impacts, which is not true. Jacksonville is actually one of the least likely places along the eastern seaboard for landfall. Historically, the highest preponderance of storm tracks passing over Jacksonville have come from hurricanes landing elsewhere in FL (even across from the Gulf). Jacksonville is about the furthest west piece of the east coast. The northbound Gulf stream is further offshore here than the rest of Florida (or Outer Banks, which is highly
susceptible to hurricane impacts) and there is a significant change in direction in the stream just south of Florida. Simplistically, that is why hurricanes move west toward Florida and are often turned northeast fairly abruptly. That is not to say Florida won't be direct hit by a Cat 5 this year. It very well may be, but the probability is low relative to other areas along the coast.
All that is to say, the insurance argument is certainly legitimate. Whether it is true or not, science will not say.