Large numbers do not make it right.
I believe the Catholic Faith is the one, true faith, but I would agree that I wouldn’t use numbers to support truth.
Case in Point: Isn’t the number of adherents following Islam growing faster than any other religion/denomination?
There are probably more Muslims than Catholics in the world (upwards of 2 Billion now) and it's growing. Yet, Jesus said, "Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it. "For the gate is small and the way is narrow that leads to life, and there are few who find it.