there's not a single PS4 game that has even come close. Looks like there aren't even any PS3 games over 2 million.
Japan loves Nintendo and portable gaming in general. No doubt about that.
However, I'm not sure you're right about Final Fantasy XII (PS3) not selling 2 million in Japan. Less than a month after its release (January 10th 2010) it had sold through (to customers) 1.844m copies on PS3 alone (just 156,000 shy of 2m).
Here we are, 7 years and 8 months later and I think it's pretty safe to assume that the PS3 version of Final Fantasy XIII has crossed the 2m mark. If someone here has access to the Media Create archives on Neogaf, we'd probably be able to find exactly when it crossed the mark.
On PS4 you have a point even though one could argue that PS4's top sellers aren't that far from 3D Mario games averaging 1.2m per game and the latest (3D World) selling 0.7m. We have Dragon Quest XI (PS4) at 1.34m but while its digital sales have been confirmed to be strong (digital made it sell "stronger" than the 3DS version at launch), I think it'll have a hard time reaching 2 million in Japan alone. Maybe Monster Hunter World will be up for the task?
FF 15 barely got to one million in Japan. I would say 3D Mario is already bigger.
I see what you're coming from but Final Fantasy XV (PS4) got to 1 million (sold through to customers) in Japan 8 months ago.
I think Super Mario Odyssey could very well outsell FFXV but let's not make it seem even more dire for the state of home consoles in Japan than it actually is.