I agree that the Wii is largely responsible for WiiU's lack of interest in both casual and core groups.
Nintendo very poorly supported the casual market it had attracted after 2010 and NoA especially supported the core quite horribly. NoJ was actually quite good with core games and NoE ported over a lot more than NoA ever did.
However as far Nintendo ruining their reputation by poor support in the later years of Wii's life, that's hogwash, as Nintendo has a long standing reputation of doing that every generation. GC was horribly staved for games during it's last 18mths and it's swan song Zelda got ported to Wii (at least Z:SS remained a Wii exclusive). Actually Nintendo's late in life support for Wii was better than GC or N64. Xenoblade, Rythym Heaven, The Last Story, Fatal Frame II, Pandora's Tower. Good to excellent games out in the last year or so. However nothing there for casuals (except for RH which at $30 for what is essencially a iOS game was just plain overpriced).
It's not all Wii's fault though. We are living in the day and age of mobile gaming. Kids 8 and 11 are all about mobile games and they go through them like junk food. Play one for a while, get bored, play the next one, then the next, and the next and the next. There's an endless supply! Free or dirt cheap! As a parent, why on earth would I buy a WiiU for my kids so I can buy, ummm... one or two games they'll play for $60 and they'll bore of them in a week. No, instead I'll give them my old smart phone or tablet and buy the latest one for myself. It just makes a whole lot more financial sense.
This is partly why WiiU upsets me, it's a piss-poor answer to this problem. So is the PS4 but the PS4 is entirely focused on the core market which will subtain it but likely, not even at PS3's level in today's marketplace.
As far as WiiU appealing to the Nintendo core, it needs some Nintendo core games. IE: Zelda, Metroid, 3D Mario, Smash Bros. The faster those come out, the better. That's WiiU's only concievable market for the next few years.