In terms of the argument on Nintendo phasing out past systems quickly or slowly:
3DS was phased out slowly because they could. 3DS had no successor. Switch consolidated their handheld and console business, but Switch was obviously a successor to the WiiU, not the 3DS. The handheld line simply ended when Switch came out. 3DS could keep being supported because it wasn't replaced, so you had a $300 Switch and a 2DS/3DS in the