I could see the argument that keeping it in a cask for 3 months does something to it that having it in the bottle those same 3 months would not - I mean, they age liquor in wooden casks to absorb flavor from the wood, allow for evaporation, and so on.
And maybe the movement (from being on a ship) would allow for some mixing so that all the contents of the cask got contact with the wood, so it’d be a bit more even (part of the same reason we stir food as it cooks).
Me, I personally doubt that the humidity is that big a deal. That, the temperature, and the movement could easily be replicated in a warehouse by putting some kind of vibration-inducing mechanism on the storage racks, and having a climate-controlled warehouse. Far more controlled, and a lot cheaper than shipping the stuff around in casks.
In summary: I could see where it makes a little difference, probably not enough to justify the woo (assuming that otherwise, the product HAS been properly barrel-aged). I certainly wouldn’t know the difference and I doubt most people would.