The Switch isn't going to be the Wii or DS. Rather more like the 3DS or GBA it will rely on the core gaming audience which respond directly to big game releases. This is unlike the Wii/DS which sold 400-500k a week on a regular basis with the motive being mostly to play Wii Sports. The Switch doesn't have that high baseline because it's a core machine.
The big downside here is that only really Nintendo release big games on the Switch, as opposed to Sony where third parties have their back as well. Not to mention Europe and the rest of the world market which Sony always has and always will dominate. Expecting Switch to do PS4 numbers in a year, let alone Wii or DS, is silly.