Why do I have to keep re-explaining this? Are people actually reading the premise at all?
Yes, I KNOW THE CONCEPT OF ISEKAI PRE-DATES JRPGS BY A LOT!!! I'm not talking about that! I'm talking about the plot of specifically "summoned from another world for the express purpose of defeating a demon king!" That plot. Those points exactly. If they go to another world for any other purpose, it doesn't count. If they go to the other world via their own power, like in the earlier Narnia example, and fight something that's not a demon king, it doesn't count.
It is specifically that plot that I'm talking about here.
EDIT: Ok, so the snow queen from the Narnia example needs a bit more in terms of qualification for this to hold up.
The objections to Narnia in particular are a few. One, the children weren't summoned or pulled to the other world in any fashion, they crawled through a wardrobe. After this, they were not greeted by a royal court or anything of the sort, they just wandered around the world exploring.
The defeating of the snow queen plot, because that's pretty much what it was, she was a reference to an earlier villain known as the snow queen from a like-named story, came about as a result of one of the children being captured by her. They were not pushed onto this quest by a force of government pleading with them to save the world.
Finally, after completing the quest, they were made rulers. This also does not line up with the standard plot.
It's not a plot of liberating a world from the demon king as summoned heroes, it's a plot of personal growth in another world, as was the case with the overwhelming majority of portal fantasy stories before Anime picked up the concept and turned it into something else.
Yes, I am using the "strip down the plot" argument to qualify FF1 for this, but you would have to remove a LOT more things from Lion the Witch and the Wardrobe (because there are other books in the Narnia series) than you would FF1 in order to get to this plot. FF1, you just have to change the name of the big bad from "chaos" to "demon king" and it basically works. Wardrobe, you'd have to flip a lot of motivations and actually ADD elements in order to get to the repeated plot we keep seeing in half of modern Isekai.
TL;DR, The Witch from wardrobe is a villain and a queen. Chaos from FF1 is almost literally a demon king by another name. Therefore, yeah, I don't think wardrobe really lines up quite that well.