Global loses players to the Japanese version, because the qol there is higher. They get more free gems (they recently gave out 10 in one day), more friend points, more giveaways and the game not breaking every day.
So, accellerated pacing to make the carrot look bigger in spite of the stick being longer.
What I don't get (this is beyond their coding ineptitude), is why don't they just make the global game the same as the Japanese version. Transition it across just a couple major updates and be done with it. Anything "skipped" with the weekly dungeons, just introduce over time like they have been. Rotate through the "new" premium units with higher pull rates daily, so there is always something fresh that you possibly don't have or want in there. Then give enough opportunities for casual gem earning (not compensated...) in order to promote the desire to catch more of the rare stuff or participate more within the game.
Sure, there is going to be a bit of backend work in there, but once in place it seems like any QOL issues should be far less of a deal breaker overall driving people to one version over another.
With how you phrased it, it made it seem to me that people going to the japanese version was a problem for the japanese developers; not with keeping the global version stable, healthy, and active.