As per the article I previously linked (
https://www.famitsu.com/news/201602/01097439.html), the President of NIS states Disgaea 5 on PS4 shipped around 112k copies overseas and doesn't insinuate those were considered poor numbers. The game's subsequent overseas sales on Switch suggests making a version of Disgaea 6 on Switch; nothing I've seen, however,
suggests there's a reason not to make the PS4 version globally available, especially since Sony would require the game to also run on the PS5.
As previously stated, my criticism is NIS creating faux exclusivity with the game. I'm honestly not completely following what you've written, but in general, I also wouldn't agree with the situation if the roles were reversed, meaning the game was regionally exclusive in the West on PS4.
You need to copy & paste the URL into your address bar:
https://www.famitsu.com/news/201602/01097439.html.