I think it's inherent to the long-running nature of the plot. We already powered up, the only things that can possibly threaten us have to be equally or more powerful than us, and then we have to beat those things. New expansion, new threat, and the cycle repeats.

If anything can be a "reset button" on our ever-increasing power level, I think it would have to be whatever lies at the end of the Hydaelyn vs Zodiark story. Something that brings us down to normal and not cosmically powerful.

Then perhaps any future expansions beyond it can start over with a less reality-threatening conflict.