Actually that’s part of the parenthetical.
Paul thanks God for two things in the passage:
1) you were slaves of sin ...
“And”
2) you were set-free from sin
That’s my point. But you put the parenthetical marks in the wrong place. Yet why??? Though what??? Theses words introduce a parenthetical.
Literally, v17 and v18 is one sentence grammatically, listing two thank you’s to God with a parenthetical in between. Which is obvious by simply answering the question; Why would Paul thank God for something God didn’t do but men did???
But thanks be to God that you were slaves of sin, but you have obeyed from the heart the pattern of teaching to which you were entrusted, and having been set free from sin, you became enslaved to righteousness.
Romans 6:17-18 -
https://www.biblegateway.com/passage?search=Romans 6:17-18&version=LEB
Or as you attempted to emphasis using parentheses versus commas:
But thanks be to God that you were slaves of sin (but you have obeyed from the heart the pattern of teaching to which you were entrusted) and (having been set free from sin) you became enslaved to righteousness.
Or
But thanks be to God that you were slaves of sin ( ... ) and (...) you became enslaved to righteousness.
Which is simply another way of saying;
So also you, consider yourselves to be dead to sin, but alive to God in Christ Jesus.
Romans 6:11 -
https://www.biblegateway.com/passage?search=Romans 6:11&version=LEB
The main (non-parenthetical) point of the passage is that Paul is thanking God (not them) for two things:
1) they were (past tense) slaves of sin
And
2) they became enslaved to righteousness.
Which is why I’ve repeatedly ask you how you got ‘empowerment’ from a verse talking about enslavement.