Your first "Q&A" don't actually relate to each other the way you think they do, which is why I felt comfortable making the post.
Okay. Here is what you originally wrote:
Shugenja are expected to be knowledgable about a wide variety of things, including other spirit realms and other spirit creatures.
That goes hand-in-hand with "being Priests."
But that doesn't mean they are designed to specifically interact with spirits other than kami just because they are shugenja. That is the disconnect, and it's something the previously quoted references doesn't address.
So I provided two separate examples (could have thrown in at least one more, but it was getting redundant and I was out of permitted quotes) of participants in the thread making it very clear and explicit that they know shugenja aren't currently mechanically "designed to specifically interact with spirits other than kami just because they are shugenja," but that they're discussing this angle because they're interested in evaluating whether making a change so that shugenja do have some benefit in these interactions would be good for the game.
Then, because you'd suggested that "previously quoted references"--I inferred from context that you might mean references to the RPG books--"doesn't address" this issue, I provided two examples from earlier in the thread of references to the books that do suggest shugenja have a special insight, and expectation of duty, relating to stuff like the Fortunes, the spirits of the dead, the Tao, etc. Those quotes from earlier posts also make clear that these references may sometimes contradict with, or at least aren't very well supported mechanically by, other parts of the RPG material, resulting in considerable ambiguity.
You now say,
Magic is not required to fulfill the "societal duties" of a shugenja. Magic has nothing to do with it. A Matsu bushi who invests enough skill points into the relevant Lore skills will be perfectly capable of fulfilling the role of the religious leader that is typically reserved for shugenja including being a spiritual intermediary .
"Spirits" in Rokugan usually aren't intangible beings that only special people can communicate with. A Kitsune is considered a spirt - it is flesh and blood. Ditto Ryu. Ditto any number of other examples one could find. And even those spirits which are typically intangible, such as gaki for example, tend to make themselves known to whomever they wish, shugenja or not.
There exists this assumed correlation between shugenja being spell casters and shugenja being spiritual leaders and, really, that's just not the case.
The reality is the fact that they are spell casters leads them to pursue scholarly knowledge related to the kami and other spirits far more than any other would, which gives them a greater insight into these matters. But, again, anyone who puts in the time and effort (and experience point investment) can play the part as well.
That shugenja are capable of communicating with the elemental kami simply gives them an edge that others don't have, much the same way that bushi have techniques that give them an edge over non-bushi in combat, and courtiers have techniques that give them an edge over non-courtiers in politics.
A perfectly fine post in itself, though it doesn't necessarily follow all that closely from your original post, which definitely did not go so far as to imply "Magic is not required to fulfill the "societal duties" of a shugenja." (I actually think that's quite a radical contention, which no one else has yet made!) If the material I reposted doesn't address what you're writing here, well, that's because this is actually another angle, making different claims and raising different questions than what you wrote before. (The mild frustration I felt while writing my post above does not, alas, imbue me with the powers of telepathy or time travel.)
So, kinda new ground at last! Yay! Though again, I felt as I read this like a lot of the foregoing discussion is still going unnoticed. Some of us, right from the beginning of the conversation, have actually talked quite a bit already about the fact that we feel like spirit-human interactions (other than stabbing) for all types of characters are neglected both mechanically and in terms of guidance like GM advice and adventure hooks, and that indeed dealing with this in a thorough way would be a big step toward solving the "shugenja problem" (always inasmuch as one agrees that such a thing exists). Examples: https://community.fantasyflightgames.com/topic/191735-rpg-shugenja-huh-what-are-you-good-for/ , https://community.fantasyflightgames.com/topic/191735-rpg-shugenja-huh-what-are-you-good-for/ , https://community.fantasyflightgames.com/topic/191735-rpg-shugenja-huh-what-are-you-good-for/page-3#entry1858944 (a non-exclusive list). So, now that we seem to be in broad agreement that this is or should be the case, any further thoughts on how to actually incorporate it better into the world and mechanical design of the game?
I'll add that when you claim there "exists this assumed correlation between shugenja being spell casters and shugenja being spiritual leaders and, really, that's just not the case," I'm not sure I can really respond well unless you bring in the bits of the books you're thinking of and define your terms a bit more. "Assumed" in-setting, or by real-world readers? "Correlation" as in an observational correlation ("humans who are shugenja are more usually than not also observed being spiritual leaders," which barring a few flashy exceptions I think is pretty hard to argue with), or as in "if A, then B" ("being a shugenja automatically makes you a kind of spiritual leader," for which I think you could make a case either way), or as in an exclusive equation of the two ("spiritual leader = shugenja and only shugenja", which isn't true but I also don't think anyone here has tried to argue it).
As to your second "Q&A," my post is unrelated to the post of yours that you quoted.
"The PCs" are the assumption because that is what we are playing as, so that is how it is going to be relevant to a player.
The longer explanation is that it doesn't have to be "just the PCs" and NPCs will be handling these issues in any area that the PCs aren't handling it in.
The world isn't built around "the player characters will handle this important cultural/social function," - The game is. That's... kind of the point of being a PC, no?
...in response to which I quoted:
-One passage asking whether, if non-shugenja PCs can interact effectively with spirits in a variety of ways, that means non-shugenja all around Rokugan also can and do--and if so, what effect that would have on the mechanics feel of the world the PCs are exploring.
-One passage from an interesting article, discussed a bit in this thread, which suggests that an important element of building a game world that truly feels "magical" is really thinking through all the magical stuff that's going on in the background even when the PCs aren't using the "magic" abilities on their character sheets.
-One passage agreeing that even when magic and magical stuff is part of the game, making sure there's some internal logic is important for maintaining the suspension of disbelief.
And I could have added others, but again, quote limits. So there you go--many participants in this conversation, in their own ways, seem to feel it's important to have a game world that's internally consistent w/r/t magic, and in which what's happening in the game --your or my particular tabletop campaign--also feels consistent with what we've been told about its world. Therefore, just saying "NPCs will take care of this when PCs aren't around" doesn't really help much, because we also need to explore what that actually means in terms of worldbuilding and game mechanics.
Finally, there's this bit of your more recent post:
interactions speak discussed this a lotTo answer your quoted post, however: Elemental kami are the only spirits that definitely do not communicate with anyone other than shugenja. Other types of spirits absolutely can, and do, communicate with non-shugenja whenever they feel like it.
As for how that reflects on the setting from a world-building point of view? All of that is already described in the source material. (ie: The day-to-day of Religion and Spirits and how they interact with the world.)