Anecdotally, it was a very confusing name and system for consumers. I worked at a game retailer during the launch of the WiiU and easily over half the people I’d try sell to would respond with something likd “Oh no, Ive already got a Wii and I don’t really need the tablet for it”
I’m glad the WiiU existed - I’m certain it paved the way for the Switch. But it was a disappointing console, released a year before a major overhaul of the gaming ecosystem (PS4/Xbone).