Romans 8 does not teach that believers are set free from sin and death.
Verse 1 ("there is therefore now no condemnation") is a legal declaration of justification. God does not overlook sin, but executes the legal sentence of the Law upon Christ as the substitute. God achieved what human weakness could not (v. 3) by sending His Son. Christ bore the penalty (passive obedience) and fulfilled the perfect moral demands of the Law (active obedience) on behalf of the elect.
So Romans 7 does describe the normal Christian life under the power of the Holy Spirit. Let me remind you once again that Paul was indwelt by the Holy Spirit when he declared that he was still overpowered by his will to do evil. The murderer and adulterer, David was also a born again believer when he committed those sins.
The conflict in Galatians 5:17 is not teaching that believers win the conflict over sin and Satan in this life. This is why you, me and every other person on the planet sins every day of our lives. You can't deny this awful truth.
Gal 5:16 is only an exhortation, it's not a command or a condition for salvation. The writer knew very well that he doesn't always walk in the Spirit, so why would he set such a condition for salvation while he knows it's impossible to meet.
I think you're reading more into my position than I've actually said.
First, I never argued that Galatians 5:16 is a condition for salvation.
Paul is writing to believers and exhorting believers how to live.
The issue is sanctification, not justification.
Second, Romans 8 does not merely repeat the legal declaration of justification.
Romans 8:2 says, "the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death."
Romans 8:4 goes on to describe those "who walk not after the flesh, but after the Spirit."
Paul is not only discussing a change of verdict.
He is discussing a change of life produced by the Spirit.
Third, saying believers still sin is not the same thing as saying believers remain in perpetual captivity to sin.
Romans 7 describes a man crying, "O wretched man that I am! who shall deliver me?"
Romans 8 answers that cry with the Spirit's liberating work.
If Romans 7 and Romans 8 describe exactly the same condition, Paul's contrast loses much of its force.
David's adultery and murder prove that believers can fall into serious sin.
They do not prove that sin remains the believer's master.
In fact, David's repentance demonstrates the opposite.
Likewise, Galatians 5:17 teaches conflict between flesh and Spirit.
But conflict is not defeat.
Paul immediately follows with, "Walk in the Spirit, and ye shall not fulfil the lust of the flesh" (Gal. 5:16).
If victory over the flesh were impossible, the exhortation would be meaningless.
So the question is not whether Christians still sin.
We all agree they do.
The question is whether the New Testament presents the normal Christian life as ongoing bondage to sin or as a Spirit-empowered struggle in which sin no longer has dominion.
Romans 6:14 explicitly says, "sin shall not have dominion over you."
That seems difficult to reconcile with the idea that Romans 7's captivity is the permanent norm for every Spirit-filled believer.