August 2020 when the game released has a peak of 19,684. The following month we get an average 7.6k players.
June 2021 when NGS release, we're at a peak of 59,197. The following month, we get an average of 7.6k players.
The game was at its lowest point in May, with at peak of 5,581. Let's say we go about re adding the peak population from initial release back to this value, just to get a rough calculation for those who may have let PSO2, but came back to NGS, that would be 14,103. So, roughly, NGS attracted give or take, an additional 45,094 players on release.
It terms of drops in the player base, we are on course to follow the same pattern as when the game initially came to the West. It is more or less indicating that the fans of the series are still sticking around, but then that also means that all the gains Sega made by attracting a new audience has been lost.
Now granted, as @Gilver-Redgrave pointed out, not all of those who played in PSO2 base had the specs to continue to play due the the graphical update that came with NGS. Still, the offset is minimal if we are on the same path as before, since any new players still around are more or less replacing those from base that cannot continue playing for whatever reason.
It is now just a matter of watching how things continue to play out. At the very least, there is a passionate base that loves the franchise that WANTS to stick around, but Sega shouldn't take advantage of that loyalty.