Automatability may make an output ubiquitous to the point where marginal value for any given output is small, but if it was really "worthless" no one would both

Automatability may make an output ubiquitous to the point where marginal value for any given output is small, but if it was really "worthless" no one would bother automating it in the first place. We automated a lot of arithmetic and then some higher math decades ago, but that hasn't meant that knowing how to do it is worthless. Effective communicative prose is an inherently high-value part of coordinating human activity. The number of roles exclusively dedicated to it might shrink but it's part of nearly every activity in a specialized society. What's most likely is that people will use it as a time-saving tool but everyone will be evaluating how good the output is and tweaking it. And that means until we're at a point where people trust AI to actually evaluate the value of AI output, many of these roles (and certainly anyone building AIs that do this) will need to know how to recognize good output -- and the training involved in that probably involves practice in personally doing it.