The battery life was completely irrelevant to me. I just kept it plugged in.
With individual devices, you can make a game where N people see something different, or N-1 people see the same thing and 1 sees something different, or where N people see the same thing (and maybe also something different, c.f. the Four Swords GBAs+GC model).
With the Wii U, you can make a game where everyone sees the same thing, or N-1 people see the same thing and 1 person sees that and something else. Even if you try to make the 1 person see something disjoint, it's too easy to cheat. And if you try to make everyone but one person see their own thing - too bad.
I always wondered why they never built something to render simple (or even complex, it can't be that costly) scenes out to multiple connected (3)DSs - relatively everyone with a Wii U must have had at least one...
especially since the switch has a touchscreen, why is the inventory screen not using it?
Thing felt like a failure the moment it was announced. Doubly so when its second E3 felt like a second attempt at the initial announce and still didn't do much to clarify what it had going for it. Triply so once you realised how limited it was.
That it took several years for games willing to engage with the platform enough to be capable of being as big of a mess as Star Fox Zero was seems like a bigger flag of its issues than the game sucking tbh. Just not an enticing format at all.