You seem to think that the term "sinless" is inextricably connected to the term "perfect".
It is not.
A person can be perfected and yet not be sinless.
When the element of indwelling sin is rendered dead within the individual (Romans 6:6, Galatians 5:24, Romans 7:8), that individual is perfected; but he is not sinless.
He still has indwelling sin; and yet does not have to walk in a sinful manner because the element of sin has been rendered dead within him.
You're contradicting yourself and confusing others. You are sticking by your claim that "perfection means perfection." In this case, it does not. To "be perfect" means to live the right way--not be "perfectly live the right way."
If you say sin is "dead within us" the way you've been saying it, then you would be saying that we are indeed "sinless." And yet, here you are, claiming that we are "not sinless." So which is it? Is sin truly "dead" within us, or are we "still sinful?"
You are ending up in this perplexity because you continue to insist "be perfect" means to "be sinless." It does not. It only means to "clean up your act and live in the path of the just," to live in obedience. It does not mean to live in obedience *perfectly!*
When the element of sin is rendered dead within the believer (Romans 6:6, Galatians 5:24, Romans 7:8), it no longer has any say over his behaviour (Romans 6:14). We are no longer obligated to obey the flesh (Romans 8:12 (kjv, NLT)).
Yes, we are to *consider* sin dead. In other words, we are to view sin as defeated *by Christ.* And so, since he's given us his Spirit, we are able to overcome every sin.
But that doesn't mean we're sinless. It means that as we live with a sin nature, we are able to deal with sin throughout our lives, overcoming the inclination towards sin continually. Sin cannot keep us prohibited, by law, from entering into Christ's righteousness.
We all have indwelling sin; while that does not mean that we are obligated to obey the flesh or to sin at any moment in the future.
Indwelling sin is a kind of uncleanness. But it doesn't have to prohibit us from walking in the righteousness of Christ. Christ's pardon enables us to partake of his righteousness despite our inclination towards sin, despite our uncleanness. He enables to walk in his path, and experience his cleansing.
It all goes back to your false association of "be perfect" with "be sinless." It is not saying that. It is saying that we should live in righteousness, period. That righteousness is the righteousness of grace. It is not the righteousness of legal perfection--otherwise, we would be condemned, separated from God, and banned forever from eternal life. We would not be allowed to live in righteousness at all!