Oh, man I disagree with a lot of this.

3D-sidescrollers are old-school hardcore games. They were what made up classic 8-bit-consoles lineup. Sure, these games can be casualized a bit, and NSMB did this a lot, but basically they aren't what draws casuals into the platform, NSMB is what a casual plays after he had his fill of Just Dance. Tropical Freeze is not casual at all, it is classic hardcore-platformer. Yoshi is in between, but didn't move much from a formula it had since ages.

You say most casuals wound up not liking the Wii in the long run, and you can't be more wrong. Nintendo just stopped to make games for them. Practically instantly. As the platform wasn't supported anymore by casual-friendly games, the sales dwindled. But the casuals didn't go anywhere. As is illustrated by the sales of Just Dance. The sales of the game stayed big even after years, and although it released on basically everything the Wii was the platform it always sold most (until Switch). And many point out just Dance sales dwindled. Yes, sure they did. It was the only game released on a platform which otherwise had nothing. It didn't change the formula. You can bet your ass, that more and more of the casual gamers gave up and moved on. But if they just disliked the Wii, they would've picked up the game on other platforms and the sales on Wii would've fallen much more abruptly. But they dwindled slowly, as the user-base was ignored over years. Think about it for a moment. You want to play a certain sort of game, and you get exactly one game a year, which is basically the same each year. Would you stay six years? Probably not, but a surprising high number did just that. The casual gamers didn't flee from the Wii, they were just ignored.

WiiU didn't emulate the iPad at all. Maybe it was a try, I can't understand it. But it doesn't work like an iPad at all. You can take the iPad wherever you want, and that is the basic appeal. And this is exactly which the WiiU gamepad cannot. So no, no iPad appeal. Just notice how the Switch actually can do that, what the WiiU-gamepad could not. Also the iPad-crowd and the Wii casuals shouldn't be lumped together. The Wii casuals were gamers, that liked to combine moving themself with gaming. The iPad-gamers are people that want to take the device everywhere. There may be overlap between the groups, but they aren't the same.

And with Switch Nintendo targeted way bigger groups than the classic Nintendo hardcore. Again, this time they actually built a machine that has the basic iPad appeal. But they moved way beyond what the classic Nintendo hardcore wants. With Zelda and Mario both they switched into the Open World craze. They built games that have a broad appeal for many groups.

I can't say that I completely agree with the OP though either. As the WiiU-ports show, the games can have a bigger audience than they had on WiiU. With the Switch though they filled the holes in the WiiU library regarding broad appeal and presented it on a desirable device.

^ so much this.

If anything I  think Nintendo didnt listen to its fans, with the Wii and Wii-u, they where aiming for casual markets instead.
I personally hated that they went from the master peice of Super Mario Galaxy --> SM3DW, it felt like a huge step in the wrong direction.
Same with XCX, while its good, its not at the same level as Xenoblade Chronicles on the Wii was.

Yeah they totally pandered to us by not giving us a real Animal Crossing, Fire Emblem, Metroid, mainline Kirby, etc... lol dude get out of here!

No dedicated Zelda. no mainline 3D Mario game or Kirby game. The versions of Star Fox and Animal Crossing we got were a disaster. Still no F-Zero or Metroid. Most odf what we did get were cheap party games that reused the same years-old assets again and again. You are wrong. So so wrong

The problem is not who Nintendo made games for or pandered to. Nintendo tried to make a system for both hardcore and casuals and made a series of mistakes along the way. Their marketing was the worst its ever been, turning off the hardcore and confusing the casuals to the point where many did not even realize it was a new console - hard to sell a system people don't even realize is a system. They underestimated how hard HD development was, causing one of the worst post-launch droughts any system has ever had and killing its momentum. They gimped the CPU, making third party development more difficult and not worth the effort after a while. And the gamepad made the system too expensive for its entire lifespan, preventing it from having the appeal of a second console the way other Nintendo consoles have had.

It was a perfect storm of bad moves that had nothing to do with whether Nintendo Land wasn't hardcore enough or Xenoblade casual enough. Many of the games that were made for the Wii U were made specifically because Nintendo had realized they were in trouble and were desperate to get something, anything out, hence why Hyrule Warriors, Captain Toad, Bayonneta 2, and Tokyo Mirage Sessions exist.

Nintendo didn't pander to anyone. That's why they didn't please anyone. Decent enough system with a lot of cool ideas but, when all was said and done, it was directionless and incomplete. It was another example of "technology for the sake of technology" while, at the same time, missing features that had become standard for the better part of a decade.

So much this. Both the 3DS and Wii U tried to recapture that lightening from their predecessors by following the same beats, and that backfired horribly. Except for a few exceptions (like Just Dance, as astutely pointed out above), the casual crowd moved on to the next hot thing. Nintendo was able to save the 3DS with a major price drop and a shift in focus, but couldn’t do the same for the Wii U. 

^This!

I mean it is right there in its would be clever but misleading name... Wii U. They wanted it to be a jack of all trades appealing to the casual family with games like Nintendoland but also having the traditional games. Sadly they didn't have their better titles available soon enough and they underestimated the next gen hardware or played into their rivals hands by having their own stuff just be small leap over the declining generation like the Wii.

The Wii U was trying to do too much for everyone and it failed to please nearly everyone because of it.

Nothing could have saved the Wii U, it was a gen behind in tech and the gimmick tablet controller idea made it a pricey device. The Wii was a one time thing type of success but it alienated a lot of people that didn't jump back into Nintendo until the Switch.

Actually the pandered to 3DS market and had no ongoing cohesive ideas for the WiiU