You're not explaining how the purportedly low bandwidth signal manages to send high quality, 60fps video streams across the known galaxy instantaneously.
Because galaxy-wide instant information transfer is a straight up fact of the Elite canon. It's just a thing that exists. Perhaps the Pilot's Federation guards the technical specifications and details of how it works to maintain their galactic monopoly on power, but it's literally just straight up "this is a thing."
If you are not happy with this being part of the lore, which it is, you should maybe consider a game that has a canon more to your liking. Star Trek, maybe?
"But what about courier missions!?" Courier missions are about transporting sensitive data that factions do not want to transfer over systems they do not control, such as (for example) GalNet, which is controlled entirely by the Pilot's Federation. Hiring a Pilot's Federation Pilot at least makes it a little less likely to be stolen, otherwise they have literally no options.
EVEN ASSUMING that such a thing as described by FDev existed, which it doesn't. There is no evidence of FTL data transmissions existing in the game-world.
The evidence of FTL data transmission is that it has been part of the Elite canon since the very beginning. Instant data transfer has always been part of Elite. It's how the game works. It's how the Pilot's Federation maintains its control. It is not only part of the lore, it is so fundamental to the lore that the game makes no sense without it.
Elite's lore was crafted around a game. Unlike Star Trek or Star Wars or whatever, where the story came first and the games came later, Elite's lore is built around game mechanics because it is lore about a game. All of this stuff you keep bringing up about instant data transfer being "just a game mechanic" is lore because the lore was specifically written to explain the game mechanic. The lore has grown as the games became more sophisticated. It has had growing pains here and there.
The entire basis of Elite gameplay is, however, that you, a Pilot's Federation CMDR, are able to do the things you do because the Pilot's Federation has instant datatransfer.
This thing you're saying about "there is no evidence of FTL data transmissions" only makes sense if you have literally never played the game, because everything in the game, literally every mechanic in the entire game, depends on this.
Crime reporting/ shooting ships/ legal vs. illegal targets: propagates via your ship's computer using GalNet
instantly and galaxy wide.
Exploration / planetary discoveries: propagates via your ship's computer using GalNet
instantly and galaxy wide.
Mining / reporting on how much things you've mined to Engineers who give you access based on those stats: propagates via your ship's computer using GalNet
instantly and galaxy wide.
Rank levels of NPCs you encounter for determining their combat ranking equivalent (they do not have an actual rank because they are not Pilot's Federation): propagates via your ship's computer using GalNet
instantly and galaxy wide.
Mission availability based on your Combat/Trade/Exporation rank: propagates via your ship's computer using GalNet
instantly and galaxy wide.
Your actual Combat/Trade/Exploration rank responding to things you do in game: propagates via your ship's computer using GalNet
instantly and galaxy wide.
System permits: propagates via your ship's computer using GalNet
instantly and galaxy wide.
In Game Communication: propagates via your ship's computer using GalNet
instantly and galaxy wide.
CQC/Arena: propagates via your ship's computer using GalNet
instantly and galaxy wide.
and so on and so on
If you are seriously convinced that FTL data transfer is not a thing in Elite: Dangerous, I would consider checking to see if you have in fact ever played Elite: Dangerous or indeed any Elite game because this is
how all of these games work.