They replaced the Wii. Had decent sales, they just were not properly supporting it anymore and they did not push for 3rd party quality. Could have went on to at least surpass the PSone in sales but they let it die.
So not obvious.
You have a point there, but on the other hand Nintendo should learn from the past. Wii could have lived longer, so as long as Nintendo remembers, Switch can do what they didn't allow the Wii to do.
But even if Nintendo went stupid again, the next transitional period between generations won't see them juggle 3-4 consoles at the same time. So even in a worst case scenario, Switch would be in a much better position than Wii to have a long tail in sales.