Well I mean look at the number of this people in this very topic trying to paint the 3DS's overall performance as mediocre and the prevailing notion in a larger sense that it represented what was supposed to be a continual decline of Nintendo's mindshare.
Point is, Nintendo's audience didn't go anywhere. They just didn't want a Wii U.
Even the failure Wii U managed to created a new big franchise for Nintendo in the form of Splatoon. So this narrative was always flawed.