I don't think using AI generator is plagiarism...
Of course it's plagiarism. Plagiarism tools might not detect or classify it as such, but AI-generated content fulfills both conditions to be considered plagiarized.
1. You are using text that doesn't belong to you and which you didn't write. A bot wrote it.
2. You aren't posting a source from where or what you got the information from.
That's why it's plagiarism.
Some time ago I had a discussion with @Lucius regarding people who have abused AI for certain purposes, especially in forums. Their silliness started when chatAI acted as a source of quality improvement, but it turned out to have a negative impact on the authenticity of the posters in the forum. I agree that the people behind the skills who use AI must be eradicated.
If you want to look smart and proficient but not from the original results of your own thoughts or writing, in the end, that person will be left behind by those who are still pouring out their content and ideas so what's wrong with never stopping learning?
For any signature spammer or for anyone who just wants to look "very intelligent" such things are a real blessing, especially for those who have alt farms with which they abuse sig campaigns. Let's say that this is perhaps the lesser evil because as you say, it would be really tragic if what some call "advance in technology" actually turns out to be something that will further distance people from each other.