Granted DS did drop off very quickly after the release of the 3DS, but Switch still has to sell more than 60 million more units from here on out to overtake it lifetime.
I can see an outside chance of that happening, if there is no Switch successor until 2024 or later, and they manage to keep up a steady stream of strong software support as well as price cuts until then, but it seems more likely to me that Nintendo will choose to keep profit margins high, that software will slow once their core teams move on to making games for its successor, or that said successor arrives before 2024, or some combination therein.
It's currently selling around 30m units a year. 60 million is not that much at the current pace. Obviously, I don't expect it to stay at this rate forever, but I don't expect it to drop off a cliff either. A super sharp sales decline would be 30m + 20m + 10m for the next 36 months, and that would total to 60m. That assumes Switch sells nothing after Sept 2024 which it obviously will. Another 60m is not that much at this point in the Switch's life.