I don't believe any of this is wrong, but "support two devices, even if in a reduced capacity, for a period, sandwiched between consistent, stable support for one device" is a hell of a lift for any console manufacturer every single time they have to do it, and the complexities of working to meet expectations for a more capable device aren't diminished. Playstations after the second are to this day mocked with memes about having no games, and this board hosts a discussion thread with doomerism about Xbox that would make even the most self-loathing Nintendrones blush. The Switch managed to pull this off by rehoming games no one bought on the Wii U while Nintendo's secondary device was the sub-HD 3DS, but these crutches don't exist for them in the transition from the Switch, an HD device with games that were already enjoyed by tens of millions.
A light back half to 2023 (which, under even the most doomer intepretations, would still be eons better than the sunsets for other Nintendo systems; third party games and substantial DLC for 10+ million sellers isn't nothing!), then, would not be ideal, but may be Nintendo's least bad option, if doing so enables them to have a stronger launch for a new system with a more solid backup plan to sell games to the Switch's install base.