Even if with grammar/spelling errors or hard to understand, good posts are still good in that they express some kind of unique idea or concept which is also interesting.

A "good post" reflects an honest attempt to contribute original thought to an ongoing conversation or discussion, even if the delivery wasn't 100% perfect. This is IMO and I think this standard is fairly accomplishable... its not a high standard.

Using AI to express dumb/unoriginal thoughts effectively will never transform a post from bad to good.

Also, at what point does the content of a post become more an expression of AI over its poster? Where do you draw that line? Using AI for writing in any way is a slippery slope that encourages laziness and unoriginality.