LOL, “quartodecimanism” had nothing at all to do with keeping the OT feasts and EVERYTHING to do with what day to celebrate Easter on.
it was a dispute among Catholics, who did not keep the 7th day Sabbath, nor the Jewish feast days.
nice try!
Your opinion is at odds with even traditional church history on just about every point.
The Council of Laoedecia, convened in 362 AD, over 300 years after the death of Christ, imposed these rules on the traditional church:
Canon 37
It is not lawful to receive portions sent from the feasts of Jews or heretics, nor to feast together with them.
Canon 38
It is not lawful to receive unleavened bread from the Jews, nor to be partakers of their impiety.
What should be obvious is that if the church had to lay down the law on these matters then it stands to reason that these were pretty prevalent practices among Christians even 3 centuries after the death of Christ. In addition:
Canon 29
Christians must not judaize by resting on the Sabbath, but must work on that day, rather honouring the Lord's Day; and, if they can, resting then as Christians. But if any shall be found to be judaizers, let them be anathema from Christ.
Same point....why outlaw it if wasn't being widely done?
And finally:
Canon 16
The Gospels are to be read on the Sabbath [i.e. Saturday], with the other Scriptures.
Note that this means that there were still some type of formal worship on the sabbath and Saturday, not Sunday, was still referred to as the sabbath. What was outlawed was resting on the sabbath, which of course was against the commandment of the Lord.