Helping you "write or rewrite something you want to convey" is already using it as a replacement of thinking.

I think it depends upon the effort involved.

Think the difference between AI saying "This paragraph seemed muddled and lacks a clear point. Consider rewriting it." vs "Here, I rewrote this paragraph to focus it more on bridging the previous and next paragraphs."

The problem with this as a metric is that it is loosely defined so it becomes quite easy for a person to twist it to justify almost any level of AI usage as "well, it is still more effort than <X>".