Launch titles matter. Where was the Wii U's Breath of the Wild? If it came out in the first year of the console's life instead of the last, it could have made a difference. Not to mention Super Mario Odyssey followed up as another hit title only about 7 months later. That was just in time for the Switch's first holiday season. Two hit games during the console's first holiday season is huge. Around 40 to 50%% of game sales happen in just November and December. Being so early in the console's life, that is going to move a lot of hardware as well.
Wii U had Nintendo Land and New Super Mario Bros U for its first holiday. Super Mario 3D World for the second holiday (and a remaster of Wind Waker if you want to include an, at the time, 11 year old game). The third holiday finally had two big hitters in Mario Kart 8 and Smash Bros. But that is already the third holiday season for the console. Basically too late at that point to make a big difference. And none of those games were the massive hit Breath of the Wild was.
Do we have sales numbers on the Wii U to Switch ports? I would love to see the numbers.
While I agree BotW and Super Mario Odyssey would have helped the Wii U sell more units, but we're talking about a console that only sold about 13 million units. Would those games have pushed it to 20 million? 25 million? Not everybody buying a Switch has Mario Odyssey or BotW. People were much more hyped about the Switch hardware in general versus the Wii U.
Basically I'm gonna stress the fact the Wii U sold horribly in spite of have notable content. If the console was closer to $199 at launch and simply used Wiimotes, I feel more people would have been willing to buy one even with the software complaints you mentioned. I don't believe the hardware ever went below $249 officially and that tablet control looked cumbersome and useless (fun fact: it was mostly useless). If the Wii U was just console and a Wiimote, it could have hit $99 to $149 at some point.
But again, it probably best the Wii U failed as it did because it was inspiration for the Switch. I'm also glad Nintendo has technically exited the home console market.
VGChartz has numbers for some Wii U to Switch ports. The Wii U had strong content that does well on Switch, but people weren't will to get the hardware.
River City: Rival Showdown for 3DS (3/5) - River City: Tokyo Rumble for 3DS (4/5) - Zelda: BotW for Wii U (5/5) - Zelda: BotW for Switch (5/5) - Zelda: Link's Awakening for Switch (4/5) - Rage 2 for X1X (4/5) - Rage for 360 (3/5) - Streets of Rage 4 for X1/PC (4/5) - Gears 5 for X1X (5/5) - Mortal Kombat 11 for X1X (5/5) - Doom 64 for N64 (emulator) (3/5) - Crackdown 3 for X1S/X1X (4/5) - Infinity Blade III - for iPad 4 (3/5) - Infinity Blade II - for iPad 4 (4/5) - Infinity Blade - for iPad 4 (4/5) - Wolfenstein: The Old Blood for X1 (3/5) - Assassin's Creed: Origins for X1 (3/5) - Uncharted: Lost Legacy for PS4 (4/5) - EA UFC 3 for X1 (4/5) - Doom for X1 (4/5) - Titanfall 2 for X1 (4/5) - Super Mario 3D World for Wii U (4/5) - South Park: The Stick of Truth for X1 BC (4/5) - Call of Duty: WWII for X1 (4/5) -Wolfenstein II for X1 - (4/5) - Dead or Alive: Dimensions for 3DS (4/5) - Marvel vs Capcom: Infinite for X1 (3/5) - Halo Wars 2 for X1/PC (4/5) - Halo Wars: DE for X1 (4/5) - Tekken 7 for X1 (4/5) - Injustice 2 for X1 (4/5) - Yakuza 5 for PS3 (3/5) - Battlefield 1 (Campaign) for X1 (3/5) - Assassin's Creed: Syndicate for X1 (4/5) - Call of Duty: Infinite Warfare for X1 (4/5) - Call of Duty: MW Remastered for X1 (4/5) - Donkey Kong Country Returns for 3DS (4/5) - Forza Horizon 3 for X1 (5/5)