It's only because Switch is a hybrid. Home consoles are on the decline in Japan, and have been from the seventh generation onward. And because the dedicated handheld market is all but dead globally, it's dying in Japan as well.
PS5 will probably sell worse than PS4 in Japan. The Xbox Series S/X will probably outsell the Xbox One, but that's a very low bar.
Lifetime Sales Predictions
Switch: 144 million (was 73, then 96, then 113 million, then 125 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima