We can't get exact data , but a big sign was the April 2021 digital charts. Returnal topped that charts with just one day of sales and that's a game that sold 6.573 in its first three days. Even if we be super generous and say that all those physical sales came on day 1 and its digital split was 70%, that still means that no other PS5 game sold more than 9,200 digital copies during the whole month.
I didn't forget, the Wii U situation supports my argument. The platform had very lacklustre first party support for quite a while and third party support dried up almost immediately. Meanwhile Switch has very strong first party support from the beginning and ,while third party support started off bad, its been growing and growing each year. The huge gulf in line up quality is one of the reasons that Switch is doing much much better than the Wii U (though of course Wii U had other problems too).
Switch is a hybrid system. Maybe its just semantics but when people say mobile I think of smartphones, not portable or hybrid consoles.
When we look a what games sell well in Japan, we see games that also sell well everywhere else. If the success of Animal Crossing, Smash Bros, Final Fantasy, Ring Fit, Mario + spinoffs, Zelda, Pokémon and Ghost of Tsushima mean "Japan has gone mobile" than every other country has as well. The only game on Japan's charts that didn't do well in the West is Momotaro Dentetsu, everything else is a global hit.
PlayStation is able to succeed alongside Switch in North America and Europe. Its issue in Japan is that PlayStation follows a largely third party strategy and Japanese third parties simply haven't been as good at putting out regular big hits as Western ones. In the West PlayStation has Assassins' Creed, COD and EA sports games coming out almost every year to drive hardware sales, Japanese third parties haven't been able to put out that kind of output since the HD era started, which is why the lower dev costs/time of portable platforms was so attractive for them. It was a lot easier for them to put out multiple FF/DQ/MH games on DS and PSP than it was on PS3.
It wasn't portable gaming that killed console gaming. It was portable games that saved that from the HD era.