The switch is doing really well, if it keeps going like this for a few years it could beat the ps4 or atleast get very close, but something everyone is not mentioning is the arrival of the new generation, right now the ps4 and Xbox are on the way out and nintendo is getting all the attention, but as soon as the new consoles arrive I wonder if the switch could keep selling so well, a price drop and mini switch could do it but new hardware will probably leave nintendo without triple aaa third party support, plus new stuff creates more hype, it will be very interesting to see what happens.
The console market is not an absolutely zero-sum game, especially considering that Nintendo is offering a fundamentally different product than what Sony & MS offer. A Nielsen survey from back in Jan. 2015 showed nearly three-quarters of PS4 & XBO owners at the time also owned a Wii in the previous generation, and both it and another survey in March 2012 indicated that there had to be a non-trivial amount overlap between platform owners. Furthermore, sales data clearly shows that the arrival of a new system in one brand has absolutely zero effect on sales of a console from another brand (though when a system gets a next-gen replacement, that does tend to eat into its sales).
While PlayStation and Xbox do have a lot in common, with comparable power and 90% or more of their libraries being games released on both systems, the sale of one does not necessarily always entail the loss of a sale by the other. While the majority of people will be satisfied with having one system in a given generation, some people buy multiple systems. I have a PS4, XBO, and Switch. In fact, the only major console I missed out on in the past 25 years was the Saturn, which had been discontinued shortly before I got my first job.
If PS & Xbox isn't an absolute zero-sum game, then the idea that the PS5 and Scarlet will cannibalize Switch sales is without any sort of basis.