Ian, the thing is the game you listed were published by Nintendo, but not made by Nintendo. They were all second party games. I also don't mind if Nintendo does more realistic things, but I don't expect...nor do I really desire it. But, lets look at one of those selections Metroid...and lets look at the games created in house at Nintendo the 2D games. There is definitely atmosphere and "edgy" "moody" feel to the game. It definitely appeals to an older audience, but nothing makes it appeal to a younger audience either.
That is the Nintendo magic. Most games created by Nintendo are fully accessible by all age group, genders, gamer group (casual, hardcore...ect) Nintendo doesn't compromise this belief...and Splatoon is a perfect example.
The game looks fun. Anyone can play it...and it creates a vibrant, fun world, anyone can be a part of. And where you say, "Look it is kiddie, and a simulation of a simulation." I say NOPE. I have never seen people in real War or real War simulations turn into squids and climb up walls or swim to pop up behind someone and take them about. Maybe to you that is childish and not engaging game play. To me it sounds fun, light, whimsical...something I completely enjoy in my video games.
Now, maybe I am harsh about the stop being a Nintendo fan. Obviously that is hyperbole to the max. But seriously, this has been over a 6-8 year trend of who and what Nintendo is. So it should not shock you.