Combining those 2, I can think of a legit reason for word spinning: to avoid identification by using
forensic linguistics. But that's not the case in any of the spam-cases we've seen.
Word spinning does a very poor job at this, since you keep the same sentence structure, grammar, etc. But still, none of the spamming accounts using word spinners are word spinning some text that they wrote themselves. They are plagiarizing.
CAPTCHA can block fully automated bot which automatically select thread at random, obtain text from AI (such as chatGPT) and then make a reply using that text.
But equally it is trivial for the bot to do all this anyway and only require human interaction for <10 seconds to solve the captcha. If you are not using Tor or something else that means you end up having to solve the same captcha twenty times or more, then one human can still mass spam with multiple bot accounts with little hindrance.
Just ban the spammers.