They are both slow, sure.
But the Vita has 4.6m in ~1.4yrs while the WiiU has 3m in ~0.6 years.
The WiiU appears less doomed imo. Also, it looks like Nintendo can make more breathing room for it than Sony with the Vita.
e=mc^2
Gaming on: PS4 Pro, Switch, SNES Mini, Wii U, PC (i5-7400, GTX 1060)