Of the 3 console developers, Nintendo had its central strategies - motion controls/extra screen; handhelds - affected much more.
While PC stands perhaps the least affected with the best graphics and arguably best controls (mouse and keyboard, or any peripherals) and mostly everyone has one anyway, the PS4 and Xbox One also partly offer better graphics than the tablets can provide for now (although as the years pass, I believe that will start to change), and - for those who care like us - controllers with actual buttons.
But for Nintendo, the graphics aren't really a big differentiator (and that is if they don't actually lose out). The 3D didn't work as well as they wanted, which could have been a differentiator had there been enough truly great killer apps that would encourage people to shell out for a 3DS even if they were mostly satisfied with the plentiful, cheap games on their mobiles/tablets.
Their attempt with the Wii U was possibly trying to catch on to the tablet success, but the success of the tablets is not really due to the form factor and control type (which the Wii U has) but rather because mostly everyone has one anyway (doesn't apply for the Wii U as it can't be used as an actual tablet) and because the games (even if they don't always hold up as a good experience) are free/cheap and fun (or at least trick people into thinking they are fun, if you think some of these f2p games are the spawn of evil psychological manipulation).
Maybe Nintendo should launch its own tablet with a variation of Android and exclusive 1st party games on it