You are absolutely right. It's possible to 'pass Copyscape' by simply misspelling enough words - really heavily spun content can still pass Copyscape. However, that content, even though it passes Copyscape, will no longer pass Google. The list of filters Google is applying to new content is growing all the time - writers need to be aware of this if they intend to squeeze every last bit of 'ranking juice' from their material.
It would be interesting to see how the ranking on the different articles differ. If you throw a few backlinks at each article (similar site, ext) see how the 5 star article ranks compared to a 2 star and 0 star article. You should try this from some cheap article producing sites like 99centarticles.com
Writing quality material is now a cost effective alternative to off-page SEO. What I mean by this is that in tests, each extra star can help leverage you up about one page. So if you had an article that was 3 star, and on page 2 for a keyphrase, spending a couple of minutes to improve it to 4 star could take it up to page 1. Something on page 10 with 2 stars can move up to page 9 with 3 stars and so on. This is one reason why it took us so long to launch the product - it was a long process getting it right by reverse engineering what was going on. The spun text detection was particularly tough, although once the principle became clear, replicating it was just a number crunching exercise. Bottom line - it's far easier to create a high quality article than it is to fool Google with fake backlinks nowadays. There are people on this very forum that can create you a very high quality article at a reasonable price (not on the BST forum, obviously!) Of course, if the material doesn't pass Google, you'd need an enormous amount of off-page stuff to get Google to rank it. If Google decided it was spun, for example, you'd need a TON of earned backlinks to make Google take it seriously (we have yet to see a convincing demo of any automated backlinking product proving it can still fool Google, BTW). I'm sure that you can still rank for absolute sh*te - but the amount of other SEO work you'd need to do FAR outweighs the easy option, which is just to rewrite the article so it passes Google. So finally, after 10 years of letting spammers run riot, Google have managed to drag the balance of power back from faking backlinks, to writing high quality material.
What you are talking about would be an extreme amount of work, because not only has Google changed for content, but also links. The backlinks need to look natural, and not a ton of them, for the ranking to be good. This also means having links from reputable websites. It seems it would be easier to pay for quality content, than spend the amount of time doing this much work. I am sure there are still buyers that are going to continue under paying writers, just as I am sure anyone with a keyboard believes they can become a writer, but I don’t think with the updates their websites will be ranking well on the search engine.
I think that there should be a program similar to copyscape but instead of copyscape it focuses on passing Google. If there was such a thing I am sure people would pay for it so that way their sites won't drop. The tool looks very interesting but I wonder about the quality of the articles & if you could tell that software was used.
It does exactly what you are requesting - it checks to see if your content passes Google, and if not, highlights the problems. As any changes you make are down to YOU, it would be impossible for anyone or anything to say that software had been used, in the same way that it is impossible to tell if a spell checker has been used - the end result of using spellchecker software is identical to using a paper thesaurus, and 10 times the manpower.
In my experience it's amazing how many people spend a ton of money developing intricate, design heavy websites and yet skimp on the most important piece of the puzzle: content. Maybe it's the hardest since it seems like you are putting your money into 'words', the value of which is hard to gauge, but I learned long ago to spend serious money for content. There is no way to get around it if you really want to make your site last.