I think an important way to understand it is how SeekingAllTruth puts it.
Did Christianity want to have the only Truth and to be the only way to God? I think the early Church and later the Catholic Church and even today many sects of Christianity want to be the only way to God.
And what does their "Truth" include? That whole thing about Adam's sin. Then add in a fallen archangel that is out to deceive everyone and get them to turn from God and get condemned to hell. Christians that believe all of that have made Jesus into the only way out. He paid the "necessary" penalty for Adam's sin. If people accept it, they avoid going to hell and get to go to heaven and be with God and Jesus.
But, as SeekingAllTruth points out, it could be that Christians set it all up to get people to obey the "God's rules"... and a few people rules too. If they want to avoid hell, then follow Jesus and obey his commandments. No other religions, including Judaism, can help them. None of them have the "Jesus" provision of dying for the sins of the world. If they doubt it? That's the devil. If they fall into temptation? That's the devil. So the "good" Christian doesn't need anything but to follow Jesus and trust in him... along with whatever the Church tells them to do too.
As usual, Baha'is put themselves in an awkward position... they have to believe in the words of Jesus but interpret them and explain them in a way that makes all religions equally true. Actually, I shouldn't say that Baha'is have to believe in the words of Jesus, because some Baha'is do question whether or not all the things attributed to Jesus were things he really said, or were things the gospel writers said he said.
Oh, but that other Baha'i explanation of "dispensation", to me, doesn't fit with what the NT writers were trying to say. If Christianity is true, then the "atoning" death of Jesus would always be a necessary thing to get people cleared of their sin debt to God. So if that isn't true, then what is true about Christianity and the NT? As you know, I believe if Christianity isn't true as believed, then it's probably made up myths and legends. I think it was meant to be exclusive and the "only" way, but... if it is myths and legends... then it isn't. But, if Baha'is want to make it somehow truly the "Word of God", then they are left with explaining away creation, the flood, Satan, hell, the resurrection and tons of other things in the NT and the Bible. Is it really worth it?