I've devoted many, many hours and paragraphs over many months and all I get in return is "LOL, nope. You're wrong," and not even followed up by "and here's why. [charts, data, reports, etc.]" 

I'm willing to bet if we can change the conditions of the bet.  (I don't want either of us playing Balan Wonderworld.)

The winner lists several games that they really, really like.  The loser picks one from the list that they haven't played yet.  Then they have to play it on normal difficulty for 50 hours or until they beat it.  The loser has 30 days to complete the task.

It's clear that no matter how much evidence I provide that some people just don't want to hear it, which is why I'm tired of arguing the point. I've devoted many, many hours and paragraphs over many months and all I get in return is "LOL, nope. You're wrong," and not even followed up by "and here's why. [charts, data, reports, etc.]" I will continue to make the point in passing should it be necessary, but I'm not going to argue it with people anymore. It's as plain as the noses on their faces, and there's no point in a constant back-and-forth anymore on the subject.

Alright, that's fine by me. No restrictions of platforms? 

Try to pick a variety of platforms if possible.  I don't want to list a bunch of Genesis games to someone who doesn't have a Genesis (for example).

Just to be clear:  I am betting the Switch outsells the PS2.

I hope not.

What Nintendo should worry about is Switch 2. The last time they thought their new brands ("DS" and "Wii") and backwards compatibility alone would bring success they got a console that sold less than half what the console that came before it did (3DS' 75 million vs DS' 155 million) and a colossal flop (Wii U), so Switch 2 is not a guaranteed success and I fear they might become complacent. Not to mention the flop that was the PS Vita, succesor to a very succesful console and with backwards compatibility, low price and portability too. Still a huge flop.

I say this because I see tons of people thinking that Switch 2 is a guaranteed success and that Nintendo shouldn't worry too much about anything. I trust them to be smart and pay attention to the market.

I see that, and the figures are A) year-to-date, B) global, and C) VGC figures. YTD figures a quarter into the year don't tell us much, global figures don't favor the DS as it had considerably different peaks in each region, and VGC figures do have a non-trivial margin of error associated with them, particularly for more granular data (their yearly & LTD estimates are usually close to spot-on, but even then errors still exist). If we counted each region separately, then the combined sales of the DS's best single year of the U.S. (2009), Japan (2006), and Europe (2008) totaled 31.26M. By comparison, the Switch's sales in the 12-month period of March 2020 to Feb. 2021, it's best 12 months everywhere, was about 23.2M in those three regions (going by NPD for the U.S., Famitsu for Japan, and assuming VGC's figure for Europe is accurate). The Switch's sales in any one region have over the past year paled in comparison to the DS's best year in those regions.

The Switch's 2021 will not beat the DS's 2009 in the U.S. It will not set any new records in Japan. It will most certainly not end with some mind-blowing 10M+ figure in Europe. And there's no guarantee that it'll be another ~28M year. Q1 is just one quarter and was facing against Q1 2020, where January & February were pre-pandemic months. 2021's real test on if it can beat 2020 has only just begun.

You're ignoring the fact that the DSi effectively displaced sales of the DS Lite. Sales of the Lite declined rapidly once the DSi was released. People just stopped buying it in favor of the DSi. We can see this in both Nintendo's shipment data as well as Media Create data, which also shows the sales split between models.

In terms of sales growth, the DSi's impact was short-lived. In the U.S., it caused a big bump in the sales when it released in April 2009, it had enough of a residual effect to put May up YoY (and #2 for the non-holiday period that year in terms of weekly averages), and it may or may not have had a residual effect in June (the previous June got a boost from a limited edition Guitar Hero: On Tour bundle, so we can't make good comparisons between those two months). But by July sales were already about back down to where they were before the DSi. The DS exhibited a strong downward trend in weekly averages after the DSi's initial release, and sales in the June-October period were down slightly from 2008. The months that put 2009 above 2008 were January (which saw a much smaller drop from December than the previous two Januaries, for reasons that aren't clear), April, May, November, and December (there were some LE DSi bundles released during the holidays in '09), with about half the year's surplus over 2008 coming from just April. Except for an anomalous YoY gain in March (people holding off for the DSi in March '09, maybe?), the DS experienced declined sales throughout 2010.

In Japan, the DS was already past its peak when the DSi released in Nov. 2008. The release of the DSi did cause a pretty big initial spike, its release week being the best non-holiday week in over a year. However, sales dropped in subsequent weeks, and the 2008 holiday season was only about the same as 2007's, and sales in 2009 were essentially flat from 2008 until Dragon Quest IX released in mid-year.

Conclusion: The DSi caused a short-term period of sales growth lasting two or three months in the U.S., and less than that in Japan. No conclusive long-term impact is obvious besides it negatively impacting sales of the Lite.

I addressed the DSi just above, but to add to that commentary, I'm talking about relative terms, not absolute terms. The DSi did help produce very impressive DS numbers the month of its release in absolute terms. But in relative terms, it didn't generate any long-term sales growth. The New 3DS caused a huge spike when it was released as well, but after two months in the U.S. and three months in Japan sales were back down to where they were before the New 3DS released.

Regarding the DS's slow start and the Lite's impact, it's not too dissimilar from the PS3, which wasn't exactly selling great at first but really hit its stride when the Slim came out. Unlike the DS and PS3, the Switch is already doing well. Do you really think the Pro will have a comparable effect on Switch sales as those revisions, pushing the Switch to even greater heights? We don't even know exactly what this new Switch model is or what it does, but even if it is a hybrid that's 4K-capable when docked, do you think a performance boost alone is going to have a far bigger impact than any other spec upgrade in history (again, in relative terms) and even many simple form factor changes?

Finally, your comparison of me to people saying Smash Ultimate was a Wii U port is not apt. There's no evidence to support that claim about SSBU, and I believe Sakurai flat-out stated that it was a brand-new game built from the ground up, so I'm not sure why anybody would make such a claim in the first place. However, I provided actual evidence for my arguments. I actually offered a causal mechanism that was plausible. The timing fit. It was an across-the-board effect, not something limited only to the Switch. It's something that persisted. There's a reason that essentially everyone that writes seriously and professionally about these things (as opposed to random gamers on message boards like ourselves) came to the same conclusion. Nobody here nor anywhere else had a better explanation or any convincing counterarguments. What little evidence provided (it was mostly conjecture that was provided) was either false, inapplicable, or otherwise didn't actually prove their point. Even if the Switch retains momentum once we are completely post-pandemic (it's still a thing, there was recently a double-shot of stimulus in the U.S., and there were new lockdowns in Japan earlier this year that coincided with a surge in demand for the Switch and possible benefits to other platforms), that still doesn't change the fact that the growth we saw was initiated by the pandemic and carried by it for many months. There is no basis to the claim that the Switch's sales would be what they presently are and have been for the past year had the pandemic not been a thing.

It's clear that no matter how much evidence I provide that some people just don't want to hear it, which is why I'm tired of arguing the point. I've devoted many, many hours and paragraphs over many months and all I get in return is "LOL, nope. You're wrong," and not even followed up by "and here's why. [charts, data, reports, etc.]" I will continue to make the point in passing should it be necessary, but I'm not going to argue it with people anymore. It's as plain as the noses on their faces, and there's no point in a constant back-and-forth anymore on the subject.