They do and they do not need Japan. PS5 will be a traditional console, because Sony has more world wide impact, however, they will lose traction over Japan overtime, but at the same time it won't matter much because the major publishers are also moving more to western focus as well, so games like Final Fantasy, Resident Evil, Monster Hunter will be on PS5.
At most because of the decline of the brand (Playstation) in Japan will attribute to lower smaller focused games moving all resources to incorporate PS4/PS5, Switch/Switch 2 and PC or complete abandon that section and move to mobile.
Precisely. The big games have all done super well on PS4, so there's no reasons for RE, FF, DQ, and MH to skip PS5. There's going to be lot of multiplatform games as Japanese developers consider the West more and more with their games.