We need these details because otherwise players will not know what to do to earn Arx and it will definitely change how people play. There will be a notion that if you do specific things it will be "worthless". And players won't travel, won't go far, won't look for asteroids too long, whatever. YouTube will be flooded with "guide" videos what counts and what doesn't. It would be great if, for a change, Frontier would be forthcoming and shared the minor details with us this time.
I think Frontier don't want us to know. They want us to play them game, ignoring Arx, and they will slowly accrue in some semi-mystical process. They don't want us to know because it will lead to exactly what you describe.
I don't think it will, in the vast majority of cases. Sure the videos will be there and there will be gear heads who have to have every paint job and earn them in game. You might have fewer players getting to triple elite or earning a billion credits. But it is inevitable, whether it is Frontier who post the details or someone else who laboriously investigates it. There will probably be threads on here swapping information on which activities generate Arx in which circumstances.
The real test will be if there is a way to game the system. Can you repeatedly dock and undock from the same station? Can you repeatedly map every planet in the same system? Does the Hutton Orbital run pay big Arx? Do you get Arx for every asteroid you scan? Do you earn for scanning the same one repeatedly?
But the vast majority of players will not be that interested in Arx. We will want maybe a paint job for each of our main ships, but £4.99 probably buys as much as we will ever want or purchases will be spread out over a few months and we will earn enough Arx to pay for them naturally. Maybe at Christmas we might find ourselves a few short to get the new shiny, so we'll spend an hour or two following the "Road To Arx" pathway.
You may think that is artificial, and certainly it could be, but it is also a new way to find value in the game. There will be players passionate about investigating every source of Arx and then putting together the perfect game-plan to earn them as fast as possible. That's adding player engagement, and that's a good thing. If Frontier has done their job, it won't change the game unbearably.