I mean this is a pretty misleading statement. The earliest Christians couldn’t call ecumenical councils before Constantine due to the fact that they were not favourable looked at by Rome. Second the debate at the Nicene Council was if Christ was pre-existent with the Father or the highest of all created things. Third, it’s baked into the New Testament that Christ is God incarnate (even books that are considered to have “Low Christology” like Mark have a pretty robust understanding – read Mark 1:1–11 in the context of the Old Testament passages from v.2,3 and you’ll see the “returning YHWH Christology” Mark presents). Finally, “earliest Christians” agreed that Jesus was God, and all the groups that disagreed were typically people trying to blend Greek religions with Christianity.