Regarding your last paragraph which seems to sum up what you have said; The statement of God's people being perfect starts in Genesis where God told Abraham to 'walk before me and be perfect.' Hebrews says we are perfected in Christ.

I don't think Paul knew anything of becoming more like Christ gradually.. In Galatians 2:20 he is essentially saying 'I am Christ and He is me.' Which is supported by Jesus' prayer that we may be one with Himself and the Father and the Holy Spirit. That oneness is described when Jesus replied to Philips question about the Father. 'Have I been so long with you Philip and you don't know me?'

Sinless perfection has cpme to be thought of as a description of wierd error. . I prefer "no more consciousness of sin' Heb 10:2

Acts 15:7-9 shows clearly that a pure heart was the result of Jesus atonement for the Apostles and the gentiles of Cornelius's household. Another way os saying a pure heart is 'no sin nature'. Romans 8 teaches the only battle with sin we now have is in the body. The final pert of our salvation yet to come is 'the redemption of the body'. A close reading of Romans 7 shows Paul was talking about sin in his body - a corrupt body which we all have to deal with. He says 'that is in my flesh'. Blessings bi