Even acknowledging that the Switch's numbers will only rise, there are still some things to note.
1. This is an apples vs. oranges comparison because Switch isn't a handheld, but a home console that happens to be portable. As such, the average console owner will buy notably more games and that's visible in the tie ratio where Switch has already exceeded the lifetime tie ratios of all Nintendo handhelds. Of course Switch is a success, there are no two ways about it. We have yet to reach the halfway point of Switch's lifecycle, yet its first party software numbers are already skyhigh.
2. Mario Kart 8 (Deluxe) has the reputation of being the best game in the series, a reputation that NSMB U (Deluxe) does not share. Software quality matters, hence why Breath of the Wild has outperformed Skyward Sword so easily. Switch games aren't going to set new franchise-highs by default.
3. Fire Emblem Fates has each of its paths counted towards the grand total, so its sales are definitely inflated because Fire Emblem fans could get the content of two games for $60 or three games for $80, so an individual Fire Emblem fan contributed up to three copies to the Fates total.
4. 2D Metroid will sell poorly if Sakamoto is allowed to continue to molest the IP. Again, software quality matters. Samus Returns on the 3DS was a 2D game that couldn't be played with the d-pad, to name just one of the things where it went wrong.