The decline brought by writing was not only in memorization. If in previous ages to understand something was to study deeply, eventually the definition may shift to having asked ChatGPT about it and skimmed through the response. This is discussed thorougly in Technopoly, which I'm still reading.

You should also consider that besides the effects of AI adoption in highly technical and scholarly people it will also affect a majority of average workers who may be more vulnerable to atrophy than others.

Not only that, but eventually AI will be native and people's perspective and usage will not be affected by previous generation habits. If people hardly bother to write their own emails, comments or essays then how will the AI-native generation approach that?

Although you make very solid points, I've been leaning to think that the AI effect on society will be shaped by the average user, not users such as yourself and the colleagues you observe in which case the doom-saying starts to make better sense.