We have no clue how much Hades sold on Steam, but based on the high amount of user reviews, I would assume it sold many millions of copies.
1) Right now, there is actually an Japan indie event happening and these devs are going all in on Steam:
https://store.steampowered.com/sale/indieliveexpo2024
2) Lots of Japanese pubs are going all in on Steam. Even SEGA stated a while ago that if they were not allowed to put the Judgment games on PC, they would abandon the IP. Atlus going all in on Steam lately. Square too.
And btw, PS5 and Xbox software is selling awful in Japan, it's all about Nintendo when it comes to software. Both Rebirth and FF XVI failed to meet expectations and they are PS5 exclusive atm.