You wrote...
But as I pointed out already, these same people take their day of rest on Sunday, which is a practice put in place by the Catholic Church; there is no authority found in Scripture for this practice.
This is simply not true.
But it is.
Despite the fact that the followers of Christ would gather to pray on Sunday, they still kept the Jewish Sabbath. (It's the reason they were getting thrown out of the synagogues.)
There's simply no instruction anywhere in the New Testament that allowed anyone to work on the Jewish Sabbath and to take their day of rest on Sunday; this was put into place by the Catholic Church.
It isn't just the Catholics who disagree with your interpretation of Scripture. Say what you will about the Seventh Day Adventists, but they are consistent about "Sola Scriptura". (They don't recognize the acts of the Magisterium in declaring foods to be clean or in declaring the day of rest to be the first and not the seventh day of the week.)
Nor is an instruction needed.
There is absolutely no NT Scripture reason for believers to worship on a particular day of the week - other than the ones I mention, foremost being that it is the Day Christ rose from the dead.
It doesn't displease God to worship on every day or one day.
No authority nor permission is needed - other than the freedom of the believer and the command to assemble together.
That later in history the Roman church institutionalized Sunday for itself is irrelevant to believers in Christ, who are not bound by anything Rome declares or believes.
Who recognizes any authority of Rome, other than romans??
As such, your argument carries no weight, except to those under the power of Rome.