Holy moly, the Wii was in it's 2009 holiday season at this point, and the Switch is roughly keeping pace with it... in March.
The gap was over 10 million just 6 months ago, now it's just 3.5 million...
Switch will beat the Wii's lifetime sales very easily, not just barely (5-15m) like you believe.
What I find amusing is how the general consensus for Switch's lifetime sales goes up every year.
January 2017: "Anything more than 50m is a highly optimistic, if not insane, prediction."
January 2018: "Okay, so Switch has been selling better than expected and 50m isn't so farfetched now, but it's still doubtful that it can beat the 3DS's lifetime sales."
January 2019: "Alright, looks like the 3DS will go down. But Nintendo consoles peak early and don't have long tails [Rol's note: a statement that is not based on complete historical data], so 100m isn't in the cards."
January 2020: "Now it's likely to beat the Wii, but it was and is crazy talk that it can match the PS4, let alone beat it."
In a year's time people will see that Switch remains ahead of the PS4 in a launch-aligned comparison and then it will hit them that the PS4 peaked in its fourth year while Switch's momentum will still be going strong. Not just because Nintendo has more system sellers in the works, but also because Switch Lite makes it easily affordable for households to add secondary and tertiary Switch units. Beating the PS4's lifetime sales will begin to look quite realistic for most people in early 2021.
And then in 2022 Switch will start to aim for the highest level in console sales history. Once it dawns on people that Switch is bound to have a long tail due to necessity - just like the 3DS saw extended first party support due to Switch's comparably high price point - so will Switch be relevant on the market even when its successor is already out. Add the revelation that in 2022 Switch's successor won't be due anytime soon and the numbers will begin to add up. Perhaps then will be the time when more and more people will question why they were content with repeating lines of conventional wisdom when said wisdom was never based on actual complete sales data to begin with. Remember last month with the rundown of sales of consoles after their respective successor had launched? It will be like that.