If Protestant denominations all disagree, are they describing the same Christ?

No, and that's the irony. If a Calvinist says Christ only died for some people and rejected everyone else, that is not the Jesus Christ we believe in, but it's not the Christ the Anabaptists believe in either. The Pentecostal says you have to speak in tongues as witness of the Holy Spirit, and the Anabaptist and Calvinist say, that's not the Holy Spirit. Then what spirit is it?

Within the denominations they reject each other's theology and each other's description of God, which shows there is a multiplicity of gods within Protestantism. Then they say, for the sake of getting along, we'll all pretend we believe the same thing, when they clearly do not. Within Luther's own lifetime you had Luther, Zwingli, Calvin, and the Anabaptists, four distinct camps, and Luther said of Zwingli something like, I hope he dies a horrible death.

Zwingli was the first to come up with the heresy that the Eucharist was symbolic. Even Luther believed in a real presence, in a different way. Luther's presupposition was that if you read the Bible you'll come to the same conclusion he did, yet he wanted to remove the book of James, so the Bible's authority was still subject to what he thought it should contain.

Both Calvin and Luther even affirmed that the Mother of God was ever-virgin, which Protestants today deny. If Luther visited a Lutheran church today, he'd say, burn it to the ground. And if you sent any Protestant back to the 4th, 5th, or 10th century, they would have seen a completely unified church: a hierarchy of patriarchs, bishops, and local priests serving the divine liturgy, with nobody off to the side.