Im kinda surprised the PS4 hasn't overtaken the PS3. It seems to do pretty ok in Japan.
Launch aligned they are neck to neck: http://www.vgchartz.com/article/440862/ps4-vs-ps3-in-japanvgchartz-gap-chartsaugust-2019/
Sony has lost a lot of trust in Japan. Maybe they are no longer in touch with japanese requirements, and Japan became a less and less important market for them. Sony focused too much on the western markets and lost a lot in Japan.
It's so bad, they sell more than double the amount of PS4 in ROW than in Japan: http://www.vgchartz.com/analysis/platform_totals/
So no, PS4 is not doing very OK in Japan. It doesn't matter so much, as the device is doing pretty well elsewhere, but Japan has become a difficult market for Sony. Well relatively speaking, obviously it isn't XBox bad.