The fact that we can understand them all and can recognize in some of them an unsurpassed artistic excellence is proof enough that not only men’s feelings and instincts, but also their intellectual and imaginative powers, were in the remotest times precisely what they are now.
The fact is proof enough.
precisely what they are now 全く現在のままで
precisely, exactly, just などが Noun Clauseを修飾する為に用いられることがある。
Tell me plainly what you want.
I don't know what exactly the difference is.