AI are actively trained to talk that way. They are trained on simulated conversations of helpful robot assistants, to sound like the robot assistant.

It is a neutral role with broad applicability. They could equally be trained for other styles. A model trained to talk as a pirate would get old, especially after it told you to bugger off when you asked for a cupcake recipe. A model trained to write like Hemingway would be frustrating when you want directions.

What would be better? who should it write like?

There is no technical challenge finetuning models to write in a specific style that is indistinguishable from a human

The 'solution' of Navier-Stokes was just for a particular set of conditions, not a general solution. If "AI" gives a general solution that's another matter.

LLMs do write in a human like fashion, it's just the median or average of everything. That's why your CEO is so impressed - it generates better writing than he can.

Take those two things together, and you've got an answer: it didn't and it does.

FWIW, I have been pleasantly surprised with the writing quality of GPT 6 Luna. It’s not particularly smart/insightful on its own, but I get good results when having it summarize or rephrase techbrospeak. It also produces coherent and easy-reading drafts from outlines and bullet points, and it generally follows instructions well in these domains.