Okay so now you're trying to obfuscate the point by focusing in on the main villian and switching from "the main questline doesn't have any of the story and narrative details that you mentioned in the optional content" too "the optional content doesn't have any of the story and narrative details that you mentioned in the main questline". Which is it wolf? You can't make both of these arguments simultaneously.
The point I'm trying to make is
integration. CoC1 has a bare-bones plot with virtually all of the worldbuilding found in isolated bubbles separate from the main story. The narrative gives the Champion no reason to interact with almost any of this content, nor any prompting towards its existence. Some of this is down to the way the game functions, but you literally stumble upon almost every event in the game via RNG rather than having the game lead you towads any of it in anything resembling a coherent fashion. I'll illustrate how this could be done better in a moment.
And the points I raised about seeing the impact of the demons on Mareth is all part of that. CoC1 runs heavily on the 'tell, don't show' model, which is how you're generally not supposed to tell a story because it's nowhere near as engaging. Again, see below.
first of all you have no specific motivation to do any side content in CoCII apart from someone coming up to you and saying "hey you mind going and getting this thing for me" or "hey have you checked out that area over there yet" and I will once again point out that having an NPC to tell you about optional content does not make it superior. Second of all while you aren't prompted to find Zetas' lair you are promted on where to find Lethices fortress by the map you find in his lair.
Here, let's use this as an example of why CoC1's storytelling is weak and how it could be improved in theory with a few little changes. As you acknowledge, you bumblefuck your way into finding Zetaz, with no motivation to do so, reason to even think he's there or reason to go exploring the cave you found. It's just 'Oh, I'm on an adventure, I guess I should go in there'. You mentioned Vala earlier, but she's someone we also don't know exists until we visit the dungeon. Now, suppose that instead of the way things play out, we encounter pre-corruption Vala
first while exploring the woods and through an event or two we get to know her and hopefully care about her. Then after her last event and some number of in-game days, she vanishes. Now we have a mystery on our hands, and then the Champ could hear from another fairy that she was taken by the demons and they've seen this cave in the forests where she's probably being held. Now we have an in-character
reason to go looking for the cave, the impact of finding Vala transformed will be much greater since we have a before and after, and we'll have one more reason to kick Zetaz' ass besides 'well, stinky demon'.
okay so you acknowledge that optional content is relevant to the story but only for companions. So none of the other NPCs matter to the story? none of them have thier lives impacted heavily by the events taking place? not a single person outside your companion group in any way ineracts with the people and world around them?
I have a hard time understanding how pointing out 'Companions interact with the story (in a way that followers/crewmates in CoC1 never or barely do)' is somehow equivalent to saying 'None of the other NPCs matter'. You're the one who asked whether any companions had relevance to the main plot.