I did not say that Muhammad was a Messenger just because 22% of the world population are Muslims. I said that 22% of the world population are not just following
some guy. In other words, there has to be a reason why that many people believe in Muhammad.
No, I do not think it is good to compare numbers and say the biggest religion is the best. Bigger is not always better.
All religions are small in the first few centuries so that is no indication that Baha’u’llah was not a Messenger of God. There were no many Christians in the first few centuries either but I believe that Jesus was a Messenger of God. The Baha’i Faith has grown faster than Christianity because we now have mass communications, but people are still the same. They cling to their old religions like a baby blanket and that is the primary reason that the Baha’i Faith has not grown faster, the other reason is that many people do not even know about it. With all the religions these days that one can find on the internet, why would they be attracted to the Baha’i Faith unless they were searching for a religion and it had what they were looking for (very rare these days) or unless someone they knew told them about it and explained what it was all about?
Atheists are nowhere near 15% of the world population:
According to sociologists ArielaKeysar and Juhem Navarro-Rivera's review of numerous global studies on atheism, there are 450 to 500 million positive atheists and agnostics worldwide (7% of the world's population), with China having the most atheists in the world (200 million convinced atheists).
Demographics of atheism - Wikipedia
I do not believe we are all Messengers of God or ever can be, although a portion of their divine power comes to the righteous man through them.
I explained why ordinary humans cannot be Messengers in my post to
Quintessence:
#45 Trailblazer,
A moment ago