I'd argue that out-of-game knowledge is required for Skyrim if you want "the best stuffz". There're some neat items hidden away that you have only a slim chance of stumbling upon if you don't know about them beforehand. Also, due to the levelled nature of some uniques (like Dragonbane) it's not a good idea to get them at lower levels (IMO a pretty bad game design), but you wouldn't know it without outside knowledge. There are also some enchanted items that have a slim chance to appear at merchants, and only at certain levels--eg Steel Boots of Muffling (only items that have this enchantment on them) that you can only realistically get from Riften (the blacksmith there has a higher chance to have enchanted items than others--again something you probably won't figure out without out-of-game knowledge) at around level (IIRC) 20 and that have no guaranteed location in game. I think I have found them only once or twice over 10 or so playthroughs.
Another example of game design that hides an important mechanics is Metro 2033 and it's hidden "karma" system that affects the ending. You wouldn't even know it was there without out-of-game sources.
Elite is not unique in this aspect, that there are mechanics you have the best chance of figuring out using out-of-game collective knowledge of the community.
For the completionists at heart (like myself) - sure, having an outside resource is good for that. But there's nothing that's tied to your character's power or gear improvement that is going to be gated behind that, you won't be hindered in terms of combat or survival or lacking in QOL or missing ways to make travel easier and so on and so forth.
Now, there
are several good reasons to use mods to address things like the levelled-item things (making them level with you, for instance), and that does require a lot of outside time and effort to bother finding all the right mods for your game... but at least that game has the option of mods to fix its game design issues.
With Metro - it's reasonable to see how in a narrative-heavy experience like that where your choices influence the final outcome with world-altering consequences, it's intentional to not spell everything out for you.
I will grant that in other similar games like Battletech, I've actually gone to the effort of diving into lua files to expose the actual effect various dialogue choices have, because I think it's lame the game doesn't warn you of the consequences that affect your crew/ship permanently & save reloading is annoying.
I think there are many reasons why Elite's game experience is not really comparable to those titles, the relative utter void of narrative devices being a rather poignant one. But you are right, the game has a lot going on that still is not explained adequately, though Fdev
have made long strides in terms of the ingame codex & information & tutorials, where there used to be none at all. I think that remains one of Elite's problems and one I'd love to see further remedied by more tutorial & codex content to address the information gap.
Yet it must also be observed it's not reasonable to expect an ingame codex to say "You should go out to one of these specific systems that have no ingame reason to be significant so you can farm heaps of high grade materials to get over the arbitrarily inflated barrier to entry to interacting with a core game & progression feature that was deliberately made too powerful to ignore". Part of the issue here is the flawed game design itself lending to needing outside 'metagaming' knowledge to be even reasonably approachable. Many such issues in Elite are tied together in these ways, which for me only reinforces the dire need to address them - any way or fashion would be better than leaving it stagnant and dormant, as has been going on for most of the game's lifetime.