Thirty-three percent does not a majority make. Within that 33% christian population, there are 34,000 sects. Which one is the right one? In reality, the statistics are probably much less than 33%. How many people do you know who 'claim' to be christian but never set foot in a church? I say it's an easy 25%. That leaves 75% of the world's population to other religions. Christianity is not a majority.
That's the real point.
Look, the way they determine what percent of the entire world is a certain religion is not accurate by any measure. It is, quite simply, bullshit. There is no practical way of telling what percentage of the world is a genuine follower of certain religions.
Just because someone was baptized as infant, does that make them a true Christian??? Of course not. 50% or more of all murderers were probably Christians at the time of the murder. I had a kid in my church who stabbed his mother to death. This kid was baptized (at around 13 or 14) and was fully integrated into the Christian system.
M*W's estimation of 25% of true Christians is around the mark, but may even be a little generous.
52% of supposed Christians are Catholic. I believe 90% of "Catholics" could give two shits about actually adhering to their religion, let alone truly believing in it.
I estimate that 75% of the other "Christian adherents" also could give a flying fuck about their religion, and don't let it influence or affect their life in any way, shape, or form.
This means that, according to me, a grand total of about 83% of all people who claim to be Christians are full of pure Grade A bullshit, and don't really follow and/or believe in the religious principles proclaimed by their sect.