Those games did save the Wii U though. Mario Kart 8 sold 8M meaning nearly 60% of all Wii U owners bought it, Smash 4U 5M nearly 38% bought it, and Splatoon 4.6M nearly 35% bought it. How much worse would the Wii U have sold without them.
Yes the Wii U failed, but what does that matter now..
Those games didn't underperform the Wii U, the Wii U underperformed those games.