Being on the Switch, with portability and being able to play with 12 other people locally in a lunchtime office space fundamentally changes the nature of Mario Kart 8 from its mediocre release on Wii U to the killer app it grew into on the Switch.

So while Mario Kart 8 did come out on Wii U, Mario Kart 8 Deluxe on Switch is a FAR better experience. You shouldn’t count the fact it began as a Wii U port against it considering how different the experience is thanks to the extra content and features - most importantly, the portability and local multiplayer expansion which turned a 7/10 game that people played 2 or 3 times after Christmas before boxing it up forever, into a 10/10 game that people look forward to playing almost daily, for years.

I certainly think 2020 was more of a lull year than you mentioned. Yes, Animal Crossing: New Horizons did release in 2020 and it was massive. But Nintendo's first-party support could've been better and was more comparable to 2018 than 2017 or 2019.

Nintendo's First-Party for 2020
Tokyo Mirage: A Wii U port
Pokemon Mystery Dungeon: A remake of a DS/GBA game
Animal Crossing: Absolutely massive
Xenoblade DE: A remake of a Wii game
Clubhouse Games; A small title
Paper Mario: Supposedly a fun game and has sold decently, but not what people want in Paper Mario
Super Mario 3D All-Stars: A lazy, overpriced collection of old 3D Mario games. Did I mention it was a timed release?
Mario Kart Live: Blurs the line between a toy and a game, expensive.
Pikmin 3 Deluxe: Wii U port
Hyrule Warriors: Fine
Fitness Boxing 2: Ok

Those are a lot of games, but how many are exciting? I like a good amount of Nintendo IPs, and only bought one of those (Animal Crossing). Usually I'll buy at least 2-3 Nintendo published games during their release year.
There were some quality third-party games for 2020, I'll admit. 2020 may have been great for shareholders, but it seemed like a lull year for a lot of Nintendo players.

Thankfully, 2021 seems better. And we probably have a few Nintendo games for this year that are unannounced. 

It was a WiiU Port that happened to be a cross-gen release. - They can be both.
Remember it started development in 2011 straight after Skyward Sword with an original planned release for 2014-2015, making it outside of the Switch's scope entirely.

It's a Port.

The fact it shares the *exact* same technical underpinnings as the WiiU version pretty much just reaffirms that.

Don't get me wrong, I enjoyed year two as well.  There were definitely some slower parts but I filled the gap with either focusing on a few PS4 games, 3rd party Switch ports, or some of those WiiU ports people complain about.  I was never in a true shortage of games to play, but none of those is what the thread was about.  When I say "lull", I am speaking in terms of exclusive content that interests me in comparison to the other years within the Switch life cycle so far.

In terms of the broad strokes, I generally agree; 2017 was amazing, 2018 was weak, 2019 was excellent, 2020... well, it was pretty good actually in terms of total lineup, it was just the pacing and communication were horrendous.

Yeah to be honest, as great as games like BOTW and Mario Odyssey are, I still feel Switch has one of Nintendo's weakest first party lineups to date, below even Wii U.

That said, it still has the next few years hopefully to change that, and I'm optimistic it will.

It's saving grace for me has been its third party support; getting to play awesome games like Witcher 3, Ori, Doom 2016/Eternal, Hellblade, Crash 4, etc, plus of course Monster Hunter Rise.

Switch has been a very nice system to me. It has a very nice library and my decision to buy one in 2029 was o point, the system already got many titles and I could build a very decent library that keep me entertained for months

Even if I like Sony and Microsoft consumers policies and overall find Nintendo business model the one more hurtful to customers I can't deny Nintendo system is the one who have the games I want to play the most. The only thing I don't like to play as much on Switch are simulators, they are better on PC, but otherwise Switch is nice for everything including indies 

I think the problem is I'm not in position to experience all Switch potential. I live in Brazil the number of Switch owners per capita is small, most of my friends don't play the same games as me, as such I find online community to play together which is not always very welcoming...

Regardless I'm still stucked at home with this whole pandemic, so while still awesome play at my bed the portability factor has been losing a lot its appeal. For context, I used to visit grandma's home almost every weekend (and generally sleep there), because it's silent, relaxed and perfect to be alone and I always bring Switch with me. Now being able to carry my Switch become ultimately pointless 

The second point is the lack of physical media and prices spike. Before 2020 there was a lot of illegal physical copies coming from grey market, after covid the influx of physical media decreased to a point software prices became pure madness, for instance I've bought Pikmin 3 for freaking 90 USD, a game that I finished in about 12 hours

Digital price also increased and since the release of the official BR eshop Nintendo does not allow me to purchase games from other countries eshops (where I could grab cheaper digital versions), the exception is America's stores, mostly just as incomplete as Brazilian eshop besides USA and Canada, so when I can't find a game in our VERY limited store (it doesn't have even 1000 titles on it) I need to buy in USA eshop and pay dollar, not really nice looking at our current exchange rates 

It's just to much less expensive gaming on PC or PS4 that I don't buy a single Switch software since January, having a good library means nothing if the hobby gets just unaffordable