That is not how it will play out.
Everyday AI writing was not a thing with GPT 3.5. It happened more around GPT 4o. And now some people are entirely comfortable with using AI writing and not even trying to hide it (while, I would agree, it's obviously still fairly garbage and easily identifiable, which helps with triggering strong averse reactions).
However the models are getting better at everything, including writing for the past years. Why would that stop now? It's reasonable to assume that the makers also know about bad writing, dislike it, and thus the models will get trained to get even better at it.
Eventually how will you be able to tell? You won't. You can't. And that goes for the rest of us. And I suspect everything will just feel somewhat nicer.
To claim there was amazing progress in the past therefore there will be amazing progress in the future is an inductive fallacy.
And as someone who gets dozens if not hundreds of AI generated emails I have to go through every day, it is _incredibly_ easy to spot which ones are AI generated and which are human written.
By its nature AI generated content is statistically consistent, the narrative equivalent of monotone speech. I don’t know anyone that can’t spot it a mile away at this point, and the more people are confronted with slop, the more attuned they become to it.