They overcame Satan by the word of their testimony. Revelation 12:11

Revelation 12:7-10 describes the victory which Michael and his angels gained over Satan in the war in heaven. But then verse 11 describes the victory of “our brethren” over Satan. The first question in this article is whether these refer to the same victory. The second question is why “our brethren” required “the word of their testimony” to overcome Satan. Why is the blood of the Lamb not sufficient?