Christianity, as a global phenomenon, is growing. In its historic centers, the Middle East and Europe, it's shrinking. That leads to the trope that this is because of (a) western decadence, and (b) Islamic predation. Or simply, (c), "our" form of Christianity is the true one, which is why God is blessing it with growth.

Those are much too simplistic, even though (a) and (b) are true as far as they go. Only God knows if (c) is true.

Will historic denominations still be around in a few decades? Again, only God knows.

But the equation of numerical growth with faithfulness is false and godless. Christian history gives us a lot of examples that contradict it, and it posits a direct interference of God in the world on behalf of one community over against another. Ask the Israelites how that worked for them.

It would be interesting to study the growth and decline in the United States of the Church of Jesus Christ, Scientist...