There is faulty reasoning here, namely the assumption that more power leads to more third party support. Yet the comparison WiiU and Switch alone disprove it. WiiU was much, much closer to contemporary consoles than Switch is, yet it got barely any 3rd-party, while Switch has massively better 3rd-party support, actually the best of all consoles. Switch may have fewer games than Steam and maybe Android, but it got much more than the other consoles. For instance in 2023 over 14K games released on Steam, but among the consoles Switch lead with 2600 games, above PS5s 1300 and Xboxs 900. So again, power is unimportant.

https://gameworldobserver.com/2024/01/12/steam-vs-consoles-catalog-3x-more-new-games-in-2023

This is true for the past as well, Gamecube and Xbox were both much more powerful than Ps2, yet the weak PS2 got the strongest 3rd-party support.

As I argued before, more power probably would've lead to even fewer games, as Nintendo would've struggled to make them. More power means higher expectations from gamers and that leads to balooning budgets, as all these objects, polygons and textures have to be created. Also a more powerful WiiU might have been more expensive.

This is why the AAA-industry currently is in a full on crash (did you see the massive layoffs). AAA games aren't sustainable anymore and I think we will see a stop or a strong slowdown in graphic showcases, as creating these games simply gets too expensive. Also both Sony and MS will go more and more 3rd-party as they have to recoup game budgets. They both have already started, this will get faster. Interestingly, by staying behind in power scale Nintendo has avoided these problems for the most part and still has manageable budgets for their games.

So yeah, anyone claiming WiiU would sell better in that scenario confuses me, as there is really no indication that would've happened. Nintendo consoles wouldn't have magically secured the 3rd-party support the company lost the generations before.

Good questions: in this scenario let's assume 3DS still exists, and the Wii U uses modern architecture with no backwards compatibility, as I don't think it would be viable to push the old PowerPC 750 cores up to that level.

The first party droughts remain.

W/O BC it would be under a different name. Thus marketing would be clear. Increased 3rd party releases. ~50m units by 2019 and totals at 52m. Switch releases Oct 2019. 

Alternate WiiU titles: Legend of Zelda: Breath of the Wild, Super Mario Odyssey, Splatoon 2, Mario + Rabbids, Xenoblade Chronicles 2, Arms, Super Mario Party, Yoshi's Crafted World
Alternate 3DS titles: Let's Go Pikachu & Eevee
Alternate Switch launch titles: 1-2 Switch, Ring Fit Adventure, Luigi's Mansion 3. Next month: Fire Emblem: Three Houses, Pokémon Sword & Shield.
Lite releases in 2021, OLED releases in 2022. New Mario Kart in 2020, New 2D Mario in 2020 (instead of MK8D+DLC, MM2), 3D Mario in 2024, next successor by 2026. Switch total shipped today would be around 90m. By 2026 around 125m.

Power/Graphics had no bearing on the WiiU's success or failure.

When titles like Mario Kart 8, Breath of the Wild, New Super Mario Bros U, Super Mario 3D World, Donkey Kong Country Tropical Freeze, Wonderful 101, Bayonetta, Captain Toad, Tokyo Mirage, Pokken Tournament, Pikmin 3, Hyrule Warriors...

It's hard to assert that graphics played a major contributing factor to the WiiU's failure when these exact games often just received a resolution bump on Switch and yet the Switch is one of the best selling consoles of all time.

It wouldn't done much better then.

The first few months of the Wii U were dreadful. The thing launched in nov/2012 and the first 'major' Nintendo game after launch being Pikmin in aug/2013, with its first real system seller being Super Mario 3D World, launching in nov/2013, more than a year after the launch. At the time 3DW was so disappointing that arguably you could say the first real system seller of the Wii U was Mario Kart 8, which launched in may 2014.

If this is still the case in this scenario, I'm not sure if better third party support would be enough for people to get a new Nintendo system; at the end of 2012 the casuals who bought the Wii had moved on and the hardcore gamers already had a PC/PS3/X360 to play the new third party releases that would come to the Wii U, so I don't see why anyone would buy a new system to play the same games they could already play.

The 3DS still existing with a very similar (albeit with sacrificed visuals/gameplay) library of first party games compared to the Wii U while being cheaper also doesn't help things.

Wiiu came out when ps4 came out so it's not really a fair comparison. Making ps4 games on wiiu would be much more difficult then  making them on Switch.

Which is why this alternate reality, the WiiU was more closer to Xbox One and PS4 specs.

So much of a console's success is the "it" factor. People don't really talk about that much, but it's true. Wii-U was seen by many as uncool and not worth their time. Switch was the opposite. For whatever reason, it was suddenly the trendy thing to own and thus... victory.

On a similar note, I can vividly remember how before Nintendo took the Wii to its first E3, everyone was making fun of it online. In every forum apart from Nintendo fan sites, people were mocking the thing. You mean to tell me it's no more powerful than a freakin' Gamecube? Are you kidding me? It's got motion controls, not normal controllers? Oh, God, what a joke! And then, when the gates of that E3 opened, we all saw these videos of hundreds of gamers literally bull-rushing over one another to get to the kiosks... and the rest is history.

I won't say it's necessarily marketing alone, but there is a certain element to that that can make or break a console. Yes, it needs to be good in its own right and have great games, but without the "it" thing, there will be no success. You have to have it. The Switch has it, the Wii-U did not. 

The Wii U had three good things about it, that I hope they bring back to the next switch. I don't anything they changed would have fixed the issues, but it did lead to Switch, which was positive.

The tablet controller in the sense that you could play local multiplayer, TV and controller. That was fun. Yer I get it, we are all online people, but still fun to sit in the same living room and play the one game. Perhaps they can do similar with Switch 2, everyone owns a console but if they all connected locally to same network, only need one copy of the game to play.

Second thing was the ease of backup updates and save files to a HDD, need to bring that back and not tie it to the console.

Third, relates to one, COD local multiplayer was fun.

The problem with the standard market for Nintendo I really think was Microsoft coming in.

If it was just Sony + Nintendo ... Nintendo could have carved out a nice and very profitable section of the market in the range of 45-50+ million units every generation out without much of a fuss. Sure Playstation would sell more, but Nintendo made a ton of money off the N64 even at 33 million units. 

Microsoft coming into the industry and doing dumb things like losing hundreds of millions of dollars made Nintendo competing for that market a bit untenable.

If XBox fades out of the market, maybe Nintendo might want to consider taking the Switch 2 chip and generously enhancing it for a home model.