You're right, it's a flaw. Sin is not genetic. Even death is not genetic. Perfect angels sinned. (2 Pet 2:4). But sin leads to death, so if everyone sins, everyone dies, because, sin's wages are death (Romans 6:23). There's nothing genetic about it. It's simply a logic problem: If x then y. If sin then death.
The word "imperfect" is not in the Bible. And, generally, when the Bible speaks of "perfect" or "perfection", it's talking about being complete or completely fulfilled, not perfect in the sense of flawless or sinless.