The transmitter on Earth can be massive with an enormous power budget. Sending from Voyager might be much more constrained: less compute to compress the payload, less power to send it.
The speed of light is obviously the same either way but it’s not obvious to me that the speed of a byte (error corrected, etc) must be.
>The speed of light is obviously the same either way
It's not obvious that it is :) We don't have any way to prove that it is the same, because every experiment to measure the speed of light going from A to B requires some light to go from B to A which cancels out any difference. We just assume that it is the same because we don't have any reason to believe it's not.
The transmitter on Earth can be massive with an enormous power budget. Sending from Voyager might be much more constrained: less compute to compress the payload, less power to send it.
The speed of light is obviously the same either way but it’s not obvious to me that the speed of a byte (error corrected, etc) must be.