I believe the conflict regarding the dating of Easter was between the Celtic church (early British and Irish) and that of Rome who attempted to imposed different dates through Augustine when he converted the pagan Saxons. Many of the Roman dates where chosen to combine with ealier pagan festivals i.e. Christ Mass with the pagan mid-winter festival; Easter with the pagan festival celebrating the Godess Eostre (hence the name) etc. The Celtic Church therefore, probably rightly considered the Roman church to be not the true church and fought for many centuries to keep what they considered the true teachings of Christ and dates for christian festivals. Remember that the Roman church was founded by Emperor Constantine the Great many centuries after Wales became a christian nation.