I don't think that conclusion is supported by Genesis. Noah's line of descent is given, but it doesn't say others weren't equally "pure" of blood.
At the very least, Noah and his sons had wives, and their families would have had to be "pure" by your definition.
The Bible speaks of a corrupt and violent culture and society being the problem, not universally corrupt blood lines.
In fact, there is very little support in the Bible, even in the OT, for the notion that God cares much at all about bloodlines. None at all in the NT.
Well it didn't take God long to get around to mentioning it. Even Christ mentioned the seedlines of the Kenites jn 8.44 and his own back to David.Rev.22.16
Genesis 3:15 "And I will put enmity between thee and the woman, and between thy seed and her Seed; It shall bruise thy head, and thou shalt bruise His heel."