First you must consider contexts and homonyms, Auto tools always fail in words with same spelling but different meanings. For instance, bark has multiple meanings, you could be referring to a tree bark while the tool would translate to a dog bark. This mistake will probably be omitted by a person who is not proficient, because they could differentiate in their writing which one they're talking about. Moreover, auto translators are hard to read and understand, could it translate idioms? Only a native speaker can interprete such things, and in literature every single detail matters.
Gradually, you are begining to admit that AI is now made sophisticated to outperform humans in translating their native language, which is a lie. Those tools are just fine for people who don't really understand the language. They'll be no way an automatic tool will translate English to my local dialect that I wouldn't find out, it's just obvious. Have you ever tried conversing with a German on social media using auto translators, how does the conversation flow?
Finally, you also failed to realize, where you mentioned optimizing your text with AI, the difference between AI generated content and AI edited contents. Take grammarly for example, there now have a beta version that helps to rewrite your text to suit native readers, AI does it, and it's far better than relying on such tools to build a content from scratch. Have you been to Quora lately, the quality of answers there dropped so much, because of AI generated contents. The rule 27 is fine the way it is, at least locals should be able to communicate with genuine native speakers of their language, the fun of natural conversation is unbeaten.
I can't agree more with you nowadays we have highly effective AI-based tools that we can convert content into humanoid translation but I think with proper knowledge and prompts we might make it hard for a native speaker to understand if the content we posted on their local board is translated by tools or not.
For example, I can take 50 posts of a person making posts here like from the Spanish board, and give these posts to GPT and ask him to learn the patterns and words and slang words being used in these posts. Now using the same pattern translate this topic for me and make it humanoid etc. etc.
AI has made things more and more easier and with proper tools which most of the people don't even aware of. So yeah the rule is not outdated but it only to be followed strictly if it is not already. I mean if they have used Auto Translation tools then the post deserves to be deleted and if they did not then there is not problem. If any native speaker could confirm, then it resolves the issue here.
PS: TBH till now I have obeyed this rule and will always follow it because it decreases the spam rate and I even try to report some if I caught exact translation.