2 Corinthians 13:11
11 Finally, brethren, rejoice, be made complete, be comforted, be like-minded, live in peace; and the God of love and peace will be with you.
I don't see anywhere in this verse a command from Paul to Christians to be sinlessly perfect. Instead, he implies that the believers in Corinth are in a process toward ever-greater sanctification which means, of course, that they were not already sinlessly perfect:
"Be made complete" not "already are made complete." Why enjoin Christians to this completion if they are already enjoying it? Obviously, Paul wrote this because the born-again believers at Corinth were not sinlessly perfect. And much of his two letters to the believers at Corinth make this abundantly clear. See above.
1 Peter 1:13-16
13 Therefore, prepare your minds for action, keep sober in spirit, fix your hope completely on the grace to be brought to you at the revelation of Jesus Christ.
14 As obedient children, do not be conformed to the former lusts which were yours in your ignorance,
15 but like the Holy One who called you, be holy yourselves also in all your behavior;
16 because it is written, "You shall be holy, for I am holy."
As in the instances above, the question that comes immediately to mind in considering what Peter wrote in this passage is "Why?" Especially if Peter's Christian readers were all sinlessly perfect, his remarks to them here make no sense. One has no need to urge better living upon those who are utterly without flaw - perfect - in their living. So, then, why does Peter communicate the things in this passage that he does? Well, obviously, because they were not sinlessly perfect. And, too, nowhere in the passage from 1 Peter 1 does Peter ever say that his readers were sinlessly perfect.
1 Peter 4:1-2
1 Therefore, since Christ has suffered in the flesh, arm yourselves also with the same purpose, because he who has suffered in the flesh has ceased from sin,
2 so as to live the rest of the time in the flesh no longer for the lusts of men, but for the will of God.
Here, as well, the same question of "Why?" arises. Why should Peter write such things to those who were sinlessly perfect? The perfect need no such commands. Implicit, then, in Peter's words here is the fact that his readers needed to be enjoined to such conduct. Why? Obviously, because they were not yet perfect in it. So it is that Peter never says his readers are sinlessly perfect and never indicates that such a state is achievable. They ought to cease from sin, yes, but he doesn't say they have ceased utterly from sin and are become sinlessly perfect. We know Peter himself was not sinlessly perfect, yielding to the pressure of Judaizers and dealing with partiality toward them, neglecting Gentile believers so that Paul had finally to rebuke him for doing so (Galatians 2:11-16).
Is Peter addressing born-again believers in his remarks above? Absolutely, he is:
1 Peter 1:1-5
1 Peter, an apostle of Jesus Christ, To those who reside as aliens, scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia, who are chosen
2 according to the foreknowledge of God the Father, by the sanctifying work of the Spirit, to obey Jesus Christ and be sprinkled with His blood: May grace and peace be yours in the fullest measure.
3 Blessed be the God and Father of our Lord Jesus Christ, who according to His great mercy has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead,
4 to obtain an inheritance which is imperishable and undefiled and will not fade away, reserved in heaven for you,
5 who are protected by the power of God through faith for a salvation ready to be revealed in the last time.
1 Peter 5:9-10
9 But resist him, firm in your faith, knowing that the same experiences of suffering are being accomplished by your brethren who are in the world.
10 After you have suffered for a little while, the God of all grace, who called you to His eternal glory in Christ, will Himself perfect, confirm, strengthen and establish you.
So it is that all your proof-texts above, upon inspection, fall well short of confirming your sinlessly perfect false teaching. This is no surprise, however, since the apostle John warned very directly about the consequence of holding to such a belief:
1 John 1:8-10
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
10 If we say that we have not sinned, we make him a liar, and his word is not in us.