History agrees with this. What we need to do is look at what transpired on the first day of the week and then look at the scriptural evidence for the assembly on the first day in the New Testament. While at the first Pentecost 3,000 were slain on this day God reversed it and instead they were given eternal life. The law kills the new covenant gives life. So did the churches of Galatia and Corinth.
Offerings are a part of worship itself.
Offerings are a part of our worship and since offerings took place on the first day of the week, wouldn't it make sense that worship also took place on the same day of the week. This is only day in the New Testament that commands Christians to give, they would have to be gathered to do so. If Sunday was not an allowable day to worship or teach on then none of this would have occurred. The number 8 is a symbol of new beginnings. Both days were used as In Ex.12.