You do realize this only goes to support what I've been saying?
"What better way to hide in plain sight than to blend with the surrounding community and adopt their ways to a significant degree?"
But the Sunday 'Lord's Day' observance wasn't adopted was it? It arose within the community, and in that sense the Christian belief in Resurrection, being the pivotal point of the entire revelation, renders the Lord's Day.
As per Ignatius: "Those who lived according to the old order of things have come to a new hope, no longer keeping the sabbath, but the Lord's Day, in which our life is blessed by him, and by his death."
"...(I)t was men who changed all that (Sabbath and Holy Days), and the change conforms nicely with already long established traditions. (*baptising them)"
Sunday was the "Venerable Day of the Sun" long before Jesus was born. Worship the sun was changed by men into worship the Son."
Quite. Changed with sound scriptural reasoning. But as Christians never worshipped the sun, that implication is not really relevant.
For pagans, every day of the week was sacred and dedicated to a god. Nor did the Romans have a 'day of rest' as such.
Certainly Constantine set up Sunday as the Day of the Sun – but he's allegiance is always arguably dubious – he's a politician, and he's looking for peace, and Christianity is a fast-growing religion, and they observe Sunday, and here he could be said to be 'going with the flow'. And, of course, for non-Christian Romans, it would be the sun – so back-slaps for Constantine all round ...