That's a long article that's mostly missing the points because it puts a strong emphasis on analyzing consoles on the basis of processing power. If you had written this article right before Switch launched, it would have ended with the conclusion that Nintendo will soon make games for PS and Xbox consoles, because Switch has less processing power than an Xbox One despite launching a few years later. Given how success and failure has played out for Nintendo consoles, processing power is a negligible factor, so it should never be more than a footnote.
The hardcore and casual dichotomy doesn't make sense either. There's a much better reason why Wii owners didn't transition to the Wii U and it's incredibly basic. If you consider it true that the Wii was liked in part because of its motion controller, then the lack of a motion controller for the Wii U console should be a big red flag. The Wii U wasn't a better Wii at all, so it's no surprise that people who liked the Wii didn't like the Wii U and it has nothing to do with being hardcore or casual. You mention in your article that the Wii U supported Wii controllers, but that's only partly true. Many games don't support those controllers at all, so the Wiimote is to the Wii U what the GameCube controller was to the Wii. Given that Just Dance 2020 will be released for the Wii, I don't think there's a strong lack of loyalty among those so-called casual Wii gamers. The problem with the Wii U was that it was a very different console in comparison with the Wii.
Your article paints Shigeru Miyamoto as a victim, but he is actually the culprit in the history of the Wii U. He had large influence in the company as general producer (the person who oversees all first party software development, including collaborations with third party studios) and got his way with the hardware for both the 3DS and the Wii U. These two consoles were designed the way they were because of Miyamoto's input and the rest of Nintendo's board of directors went along with it because the company had been very successful in the years leading up to those new consoles. That's correctly described as overconfidence and the Iwata Asks for the 3DS hardware reeks of it because the talking heads were sure that 3D cannot fail. I view Star Fox Zero as Iwata's punishment for Miyamoto; the latter insisted on the Gamepad, so Iwata put Miyamoto's name on the line by explicitly telling investors that Miyamoto will make use of the Gamepad. That was in public, but behind closed doors Miyamoto had already been excluded from working on the future Nintendo hardware, that's why Miyamoto's name never came up in anything Switch-related. Shinya Takahashi took over as general producer and Miyamoto has been promoted into a more or less retirement position because that's how the Japanese handle this.
The initial software drought of the Wii U is a consequence of the initial failure of the 3DS which required the reallocation of manpower to get 3DS games out faster in order to get 3DS hardware sales back on track. Getting certain games done faster meant that something else would take longer, so the Wii U suffered for it. But it shouldn't be forgotten how braindead Nintendo's announcement strategy was for Wii U games. At E3 2012 they deliberately held back with only four first party games and gave a lot of spotlight to third party titles because of the misbelief that first party software hurts the sales of third party games. With barely anything to look forward to, Wii U sales tanked quickly and Nintendo reacted promptly with a January Direct to announce a plethora of first party games that were in the works, including games that ended up releasing in 2015 and 2016.
What essentially all mistakes with the Wii U come down to is listen to the wrong people, be it Nintendo's own general producer, the executives of AAA third party publishers or the hardcore gamer chatter on the internet. The people that were ignored were the ones who were actually buying Nintendo hardware and software.
Lastly, the consolidation of home console and handheld software development would have happened even if the Wii U had had respectable sales. The 3DS was off to a rough start because the development times for games were increasing and that would only get worse, so another generation of supporting two distinct platforms wasn't going to be feasible. The even rougher launch year of the Wii U reinforced that, so in early 2014 Iwata already talked consolidation of software development. What is often overlooked or forgotten is that Sony implicitly announced at E3 2013 that they were going to exit the handheld market, so that's another big factor for Nintendo's decision. Nintendo having to support two distinct consoles when both of their competitors have only one console each would be a herculean task.