As has been previously noted in this commentary, the ordinance of baptism is not explicitly an important aspect of Nephite religion until Alma the Elder. By the time his son is speaking, the ordinance has become definitive, such that the Atoning Messiah has his mission only to the baptized. What this means is that the ordinance of baptism has completely supplanted the Jewish sacrificial atonement. In the development of the gospel in the New World, there is clearly a movement away from the sacrificial cult of Israel and toward a more spiritualized worship that is much more reminiscent of Christianity and even Israel after the destruction of the Jerusalem Temple by the Romans.
It is even quite probable that the physical separation from both the physical temple in Jerusalem and the particular lineage of priests that were to officiate in that temple led to the similar response in both the Old World Christians and the pre-Christian Nephites in the New World.
In any case, by this point in time, Alma firmly states that the Atoning Messiah is coming to “redeem those who will be baptized unto repentance.” There is absolutely no indication that there is any other sacrifice required. The religion has been transformed into the same spiritual relationship to God instead of a sacrificial one that occurred in Israel in the aftermath of the temple’s destruction.