I wouldn't worry about the Switch at all in 2020. I believe very much that it will be the #1 selling system again for the next year. Next gen consoles typically take a year or two to start selling at a rapid pace. There is also budget to take into consideration. These new consoles are likely to cost $400-$500 and for that kind of money you can buy a PS4/Xbox 1/Switch with several games and many will still do that for a couple years.
Nintendo has never had to rely on 3rd party support to sell their systems. Sony/Microsoft heavy reliance on 3rd party games is a detriment IMO as it does not create brand loyalty. You can see that with the last few generations (Xbox 360 being "more popular" than the PS3, the PS4 being "more popular" than the Xbox 1) and Nintendo has never really suffered that (the Wii U was just a major misstep as a whole and had nothing to do with 3rd party support).
Nintendo with the Switch:
