Define what you mean by fly more efficiently. I'd like to see some numbers on efficiency.
Lift to drag ratio describes the aerodynamic efficiency of the vehicle. Typical values, depending on flight conditions, are 4-5 for a helicopter, 8-13 for small planes, and 12-16 for our airships. (Large planes can get as high as 17, but a larger airship would be also be even more efficient). https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Examples_of...
From the L/D ratio and the propulsion system efficiency you can calculate the total energy used, and divide that by the payload mass to get energy/kg/km.
Sure, I don't doubt a blimp is more efficient when the wind is blowing it to where it wants to go, but what happens when the wind doesn't cooperate?
EDIT: yes, the Wikipedia page states that L/D numbers are usually presented as graphs, because they are dependent on speed. This means that without knowing the wind speed the blimp is facing, especially given it travels at a lowly 35 MPH, you can't really calculate an L/D number. For the helicopter and airplane, the wind matters less as they are going much faster.
The figure of merit is maximum (speed * L/D), not L/D alone, and this is where the efficiency of airships fall apart. Due to their greater parasite drag compared to aircraft (necessitated by the lifting gas volume), airships generally can’t match the same per mile efficiency, and even if they can, not at the same von Karman efficiency.
L/D is a ratio of forces, and work = force times distance. Going faster at the same L/D decreases the travel time but increases the power used, for the same energy usage. Generally L/D depends on speed, but you can get an apples-to-apples comparison of the energy usage of two different aircraft by comparing only L/D.
I think we might be discussing two different figures of merit. The efficiency that I care about is "energy per lb of payload per mile." You haven't defined what you mean by "efficiency per mile," but from the reference to von Karman efficiency, I think you have a figure-of-merit in mind that includes speed - specific resistance or productivity or something like that.
But the economics of our vehicle and use case don't really change with speed. The middle mile legs that we're flying are not fully-utilized - the most important thing is to get the cost per flight down, so that we can dispatch the aircraft whenever there's a delivery ready.