The problem with this approach is that...
So I see your logic, I really do. However it does not work nearly as good in practice as you think it does in your head. If that is all you have to lean on, you will almost certainly be proven wrong in the end.
Good points and yes, my statement was more general. There are other factors but considering they are (or appear to be) aiming for the Switch to be both their handheld and home console, it stands to reason the market isn't just handheld or home, it's both. Add in many DS buyers aren't really going to buy a Switch as they weren't gamer gamers, and have since moved on to mobile.
Over 100 mil is easy I think, depending on the lineup and other factors, I can also see people buying multiple units as well, so nearing 150 could be a potential number.