We are not justified by any law keeping, we keep the commandments of God through faith. I personally don't see 1Cor9 as freedom to break any of God's commandments, so perhaps I am misunderstanding you as I know this is not what you teach.
A better equivalent is saying you must wash hands before eating and keeping Sunday worship. Neither are a commandment of God. Jesus said we need to obey the commandments of God. Matthew 15:3-9
In 1Cor9 Paul describes the freedom he has in Christ to be with Jews and not be as a Jew (even though he is of Israel by race). He has the freedom to be with those without law (or lawless ones) to win them - then he makes sure we understand the limits of this - he cannot be as lawless to God and in parallel, he must be lawful to Christ.
I'm simply not fully convinced that I can't be with Jesus picking and eating grain from the fields on Sabbath, that I have to avoid doing needful good that may arise on Saturday as Jesus did because He saw His Father doing such, that I can't be among the lawless to win them on Saturday, that I was made for Sabbath instead of Sabbath being made for me, that I see Saturday as a needful day to stop everything I'm normally doing for the 6 remaining days to recall He is the Creator or the one who brought Israel out of Egypt or saved me from slavery to sin, when most of my days in any given month or year(s) are mostly redeemed in His Word contemplating and studying Him as Creator and God and my Father and my Lord and my Guide and the Root I'm attached to so I can produce, and the Foundation of the structure I'm a part of, etc...
You are much more versed in this topic of Sabbath than I am. For me to share or Scripturally critique the SDA view in entirety, I would have to go through it in entirety. I have listened to a fair amount of SDA instruction on this subject, but I know there is much more. I found the SDA instruction about Sabbath vs. Sunday very informational. My original concern for Sabbath vs. Sunday was not SDA, but more Messianic. IOW, I did not see what stemmed from Rome to be truly Apostolic and truly replacing the Jewish foundations of Christ's
Ekklesia. I've mentioned before that the best congregational experience I've had was the few years prior to Seminary attending a small Messianic Jewish Temple on Shabbat. It was a small group, with a knowledgeable Rabbi, they recognized & understood Messiah and identified Him portrayed in the Jewish Holy Days and throughout the Tanakh, and in observing certain days taught how He is portrayed in them. Among other things, attending a Seder with them was very special, as was each Sabbath.
I guess for me it kind of boils down to this now, SabbathBlessings, I don't trust my spiritual life in Christ to much of anybody anymore. I've been blessed with the time, desire, and sufficient resources to have devoted the past 3+ decades to my pursuit of knowing Him from His Word in Christ in Spirit. Virtually every time I have attended some group in any denomination or have had some fairly extensive discussions with anyone from such groups, I have always been left with the thoughts compared with Scripture that they don't know as much as they profess to know. Beyond that, IMO I was extremely mislead by the theological camp I received my initial training in. This was not intentional. They were just good camp-based soldiers.
At this point, if He makes something clear to me in Scripture, that I do. If there is anything unclear, that I do not take as being fully responsible to do. If He uses someone to convince me or to show me something I'm not seeing, then I hope I'm paying attention and not closing myself off. But I have been trained to read His Text in some detail and much of what I take in from others when I may venture out to see what's being said about some Scripture or Scriptural topic, is at exegetical levels not
normally discussed in churches or by those who get their instruction from most pulpits. So, I scrutinize what I'm being told by any person, no matter who they are, no matter how scholarly they think they are or are recognized to be, or how knowledgeable of Scripture they or others think they are.
I hope this is clear and informational. I've respected your point of view and when I might read debates about Sabbath I remain open to any input that may interest me, although at this time, as you know, I don't want to argue about Sabbath or Eschatology. For a bit different reason, I'm getting to the point where I may stop discussing a summary command containing vs. not containing the points it summarizes. I'm sure you know what I mean by this.
With respect.