Using VGC numbers, first 24 months for PS4 and XBO show 9'9M for PS4 and 8'8M for XBO, when Switch is already at 10'5M with 22 months. Switch should probably be around 11'5M in its first 24 months. PS4 needs 25 months to reach 11'5M (XBO 10'3M in the same period), being 12'6M with 26 months, 16 jan 2016 (XBO 11'2M in the same period). Switch should probably around the same as PS4 with 26 months (begin of May 2019).
All of those consoles did impressively well in USA whatever you want to count them, first 12 months, first 24 months, first 26 months, 2014-2015 PS4/XBO vs 2017-2018 Switch, ... This shows too, that Microsoft has to do something outside USA, because is the only reason they are not competing against Sony and Nintendo.