I have included in red some low prediction for a less than 19M (18,88) fiscal year 2018 for Nintendo.
Here we can see that the Switch still hold done well against the PS4 even starting with one Q3 less.
So you are comparing the switch with the wii and thats how you came up with that 2.5 10.5 4 million number? Yet ignore that the wii started the year with a strong 5.1 and 4.9 million while the switch is starting with 1.8 million. I know pokemon and smash are popular but 10.5 seems a tad farfetched. We will see I guess but I would be willing to bet money it will be much lower than that.