As a small mention, 2015 was a bad year for the 3ds. Aside from a couple Zelda games, niche JRPGs, and mediocre games like Chibi-Robo, there wasn’t a whole lot going on for the system; its sales success that year mostly came from the New 3ds model that released.
A new Nintendo era was ushered in by the Switch; the Nintendo faithful could raise their heads after years of embarrassment as the Nintendo Dark Ages were over.
Super Mario 3D World does not hold a candle in terms of sheer brilliance, and elevation of the series to Super Mario Galaxy
Mario Kart 8 didn’t change the series as much as Double Dash!! or Mario Kart Wii
Smash Bros for Wii U did not come close to having the same amount of content to Brawl. It didn’t even try to include a story mode.
Yoshi’s Wooly World was practically the same as prior Yoshi games, just with a new coat of paint (or yarn)
Star Fox: Zero could never come close to Star Fox 64
I disagree with 2015 being a bad year for the 3DS. Critics loved that year with Majora's Mask, SMT: Devil Survivor 2, Etrian Odyssey Untold 2, Xenoblade Chronicles 3D, and Monster Hunter 4 Ultimate.
As far as sales go Monster Hunter 4, Yokai Watch, Majora's Mask, Tri Force Heroes, and Pokemon Super Mystery Dungeon all sold over a million units.
I still remember the thread here when Switch was announced. So many of us here were so badly beaten and berated, that we were all sure the Switch would fail. I thought $300 was too much to ask. People looked at Mario Kart, and Zelda as the only launch window titles, and proclaimed "Another system with no games!".
I completely agree with you on how lazy 3D World, Starfox, and Whooly World were. Those games were just dissapointing. 3D World clearly started out life as a 3DS title, and was changed over to a Wii U game once Nintendo realized how badly the 2013 drought was getting.