The way the post is written, I wonder if the author is working for a company going through a growth spurt and where, through sheer size, everything is becoming more "corporate".

There's a huge difference between having AI clean up a text you send privately to someone you have worked closely with for years, versus a broad spectrum text sent by a VP to hundreds of people or more. The first case is reprehensible, for the reasons the author lays out. But as for the second case, corporate doublespeak has been a meme since long before the advent of AI and it would remain even in some AI-pocalypse. Just because your boss puts out sanitized language in a mass communication, doesn't inherently mean your boss won't still be present and real with you in a more private setting.

I wonder if the way that LLMs write - the super generic, soulless communication - is also due to them being trained on public communication.

Yes, the more personal the context, the more the humanity aspect / being relatable matters.