No, its the opposite.

PNW accent is basically what happens if a whole bunch of Americans with originally different accents from different regions all try to cross the great divide either by wagon or train, to find either farmland or a ticket to the Alaska gold rush…

And then everybody who isn’t dead after the attempt more or less averages out their accents into a rough middleground.

Some linguistic evolution has been going on since then, beyond that, but thats what I mean by end point; the PNW was the literal geographic last stop on the physical colonization of the contiguous US.

Only thing that might be more ‘final’ than that would maybe I guess be Alaska, but I do not know much about an Alaskan accent.