People really need to learn to take a step back and stop looking at every single business decision from the perspective of a hardcore fan (I believe most of us fall in that latter group).
Us fans will already buy the game. No matter what they show or do (or don't), we're there day one (raise your hand if you've already pre-ordered and even paid for the game*). This demo isn't meant for us. In fact, a lot of marketing material surrounding XV hasn't been for us.
Every thing they do has a very specific goal and target audience in mind. Even if we think it's a stupid move, there's still a rational behind it from their perspective.
There's enough doubt and confusion present in the Japanese market regarding this game and said doubt is centered around a few aspects. This demo is aimed to address (a few) of those aspects. The difficulty of the game is one of them.
And no, when talking about "Japan" it's not meant as a generalization. The Japanese gaming market is insanely huge. What I've written about hardcore gamers also applies to a large group of Japanese gamers. They're already there day one together with us. This demo isn't aimed at them either. So no, "Japan" isn't suddenly bad at games because the gaming market is huge there. There's an immensely large more casual gaming market there to which a story-driven, beautiful-looking and wonderful-sounding game appeals to, while they might not be skilled enough to tackle the normal difficulty of the game. This is a huge market as well and SE is trying to tap that market.
In the end, it's a good thing they're doing this because it can potentially lead to much more sales and that's good for the future of FF.
*Bought the Pro and PSVR yesterday, have the Deluxe Edition of the game pre-ordered since around the Uncovered event.