Dan wrote:
"---of course at that point you could just run open wire line to any
distant receiver."

Yes, if it isn`t too distant.

If the 1000-mile open wire line lost 0.1 dB per 100 feet, loss would be
52.8 dB per mile or about 53 thousand db in its entire length, hardly a
useable transmission line.

On the other hand, suppose the wavelength were 160 meters. In the first
wavelength of a radio signal radiated in free space, you would lose 22
dB. In the second, you would lose an additional 6 dB. Doubling the
distance again to a total of 7 wavelengths, or 1120 meters, total space
loss would be 34 dB.

At a distance of 2240 meters from the transmitter, the loss is 40 dB
which is less that our open wire line would lose in its 1st mile, a
shorter distance.

Every mile of wire line extracts the same loss. Very long wire lines
become useless without repeaters to boost signal above the noise level.
Doubling line-of-sight radio path distance only increases path loss 6dB,
no matter how long the path is.

As for efficiency, J.D. Kraus says:
"The efficiency of an antenna is defined as the ratio between the power
radiated by it and the power delivered into the antenna." (page 866 of
3rd ed. of "Antennas".

Best regards, Richard Harrison, KB5WZI