Every MMO/MO that doesn't introduce massive grind walls can be completed fast. I completely disagree with takes such as it meaning that you've completed this content update and there is nothing to do but play something else. It depends entirely on how long you're entertained by doing whatever is available in the game, even just the social side. Then when you're truly feeling like you've had enough switching to another game is inevitable, but it's more probable it will be some single player game or similar from my experience. One of PSO2's strength is how easy it is to pick up and play with rather minimal time investment so you don't feel like dropping it altogether just because you've not logged in in a year or two.
There is no better choice for PSO2's fate either way. Anyone who is new or still hasn't accomplished something he wanted in PSO2 can play it to the heart's content. The only other option is releasing content for PSO2, but that means that content isn't released for PSO2 NGS. What would that accomplish? Trying to make players who weren't interested in PSO2 go through all the level 1 to 100 grind?