The "Switch sales will drop off now they've used most of their big IPs" theory has been going since late 2017, it was wrong then and it's wrong now.
It's also a mistake to assume Switch will necessarily follow the sales trends of past Nintendo systems has it is quite unlike any of its predecessors.
I never said the Switch Hardware would drop off due to their existing IPs already being on the platform, I said new games will do little do boost hardware. The Switch hardware dropping off is projected from other Nintendo hardware. Of course impossible to know exactly how the Switch will age but as time but what is the argument against a Switch 2 offsetting this (outside of, they can continue to sell Switch 1) because they can actually just do both. All the meanwhile benefitting from software which you complained about being missing a few months back.