I would say that right after Pentecost is when some in the Church started their false doctrine....so I would consider your above statement factual....regarding "{some}" in the early Church. However, it is very clear by reading "other" early documents, as well as scripture, that the Apostles, including Paul, continued to celebrate the Festivals and Sabbaths of the Lord. To be fair you have to ask yourself, "Why did it take hundreds of years before the "Church" outlawed Sabbath keeping and the observance of Festivals if it was established doctrine to do so by the Apostles?"
Multiple times in New Testament scripture are we warned of false prophets and false doctrine. Therefore it is incumbent to your argument to give us chapter and verse showing the changes you insist occurred....being scripturally stated. This you cannot do....and frankly, I'm am very surprised that you folks hold to this doctrine under these circumstances. After all.....the only reason you folks celebrate "The Venerable Day of the Sun" is because you say that was the resurrection day.....and this argument is so pathetic I don't even think you actually believe it. I think you are just caught in the trap of the "Catholic Sabbath" and don't know how to get out.
You say "Catholic" like it's a bad thing.