5M seems less likely than 2M difference.
2M is probably the difference in December alone with Pokemon and Animal Crossing. And even with just Pokemon, it should still do that difference.
Last year the PS4 lagged over 2M behind in December already (2.07M according to VGChartz), so how do you expect this year to do any less than that?
It is quite possible that by October the difference is less than 2M, but during the last 2-3 months the Switch should massively outsell the PS4.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
List as Google Doc: https://docs.google.com/spreadsheets/d/1aW2hXQT1TheElVS7z-F3pP-7nbqdrDqWNTxl6JoJWBY/edit?usp=sharing
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/