That’s really weird. I have tested WordAI and Spin Rewriter with Copyscape and the results were always 80%+ uniquness, even 90%+. I don’t know how u spun the content to achieve such low results, but this is definitely way too bad. As for the block spinning, I have to be honest, this is the first time I’m hearing of it and I will have to check it out when I have a bit of time, but generally, yes, in the best case scenario, you would manually touch your Tier 1 content to make it 100% human readable and as unique as possible. For lower tiers, you can do pretty much anything, but again, the better quality of content, the better results you will have. That’s in my opinion and experience. 

If you are someone who is trying to have a proper understanding of the functionality of an article rewriter or a paraphrasing tool then you are at the right place. An article rewriter tool is a simple tool that can work both online or offline, depending on how it functions. An instant article spinner or a paraphrasing tool is an efficient yet very easy to use tool that understand and identifies the text you give it, then rewriting it for you. It enables you to get your article rewritten with no trouble. Any quality article spinner saves your time and the trouble of sitting in front of your computer for hours in an effort to write unique and quality content. However, article rewriter is only a tool that does exactly what you asks it to do that means it only rewrites the content you give it, you still can go through the rewritten content make any changes that might be needed. At times, a paraphrasing tool ends up rewriting an article that doesn’t make much sense and that’s why it’s essential to proofread before you use the content.
When you integrate Perfect Tense with WordAi, Perfect Tense will check any text you spin for grammatical errors. Perfect Tense will then add those spelling and grammatical errors as synonyms. This means that your spintax will be more unique and more readable. When using Perfect Tense with WordAi, your spun content will often end up even higher quality than the original. 

Any article rewriter or paraphrasing tool basically scans through the content you provide it in order to look for all the words that it can replace with suitable synonyms or substitutes. Every replaced word will appear bold and highlighted in a colorful text. Clicking on the word will give you details such as original word or other suggestions, you also have an option to add your own word.  By clicking on the original word, you can go back to original.
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.
Other article spinners also require that you enter your own custom synonyms manually or individually approve lists of potential synonyms as they are presented to you. This is another way of expecting you to do most of thinking, as opposed to expecting the software to be smart enough to instantly make judgment calls for you. Thus, one of Spinbot's main goals is to make the article spinning process as quick and painless as possible.