LLMs are not very good at generating ideas - unless you ask them to go crazy - then they can generate interesting ideas that quickly become repetitive. But the initial set is actually good in my own experience.

As for writing, we need to keep in mind that LLMs are tools that augment. So yes if you completely abdicate all responsibility to the LLM that is basically not constructive at all. But if you use it as a tool - what difference does it make? Spell and grammar checkers are also changing your text and of course I am exaggerating a little.

And I do think LLMs can help you think better but not in a default mode. It is not about prompting skills but making it work the way you want it. And that takes time because well, it is not deterministic and it requires understanding how you generally think and write. Most of the time might not be possible. For others it works really well, maybe because they write like an LLM?

Btw, we often forget that English is not native for majority of people on this planet.

IMHO using LLMs to express themselves clearly is many times better than remaining misunderstood.