Sorry, but what completely changed the disciples was not "crabgrass in a cemetery." It was a meeting with Jesus risen from the dead. Otherwise no one would have heard about another Jew nailed to a cross. Nothing extraordinary about that.

The substitutionary atonement theory dates from the 11th century, and I am sure that St Anselm who devised it would be shocked by how it is misused to manipulate people.

As for remaining in our sins if Christ be not raised from the dead, that doesn't mean he died to take our sins upon himself .