Imo it is not possible for google to detect properly spun content, it is not worth computing power it requires. They can do this using ngrams for example, but it is uses a lot of queries. And for example article spinner I coded beats this algo, so google cant detect that the content is spun. Manual spinning is also good but it takes more than 30 minutes per article.

Great article and research, thanks so much. I was looking to speed up some of my content writing but these are pretty bad. All of them do awkward things that would require proof reading and replacing words and phrases to be published. This was a simple short story, very readable. Professional industries with inelastic terms and vocabulary would not fare well. Just this one paragraph felt like a lot of work to fix. I’ve heard a lot about spinners and SEO, but now I see that it would not work in a professional industry, unless I’m judging to quickly without trying them, let me know. I don’t see business or legal content doing well with these.
I've ranked websites in the past with spun content, and now they are still on #1 position of google. First year (2014) google found me because my spun was really bad, many paragraphs were just copied and my position drop from #2 to around #20 after a panda update. Later I cleaned all my text with better spun (I didn't buy any article!), my ranking went up again, and with more backlinks I reached #1 and it is still there
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