First of all, you are making an assumption regarding my thought process.
For the sake of intellectual discussion only, postulate with me that Deity exists.
Now if Deity exists then Deity determines what religion is acceptable to Deity and what religion is not acceptable to Deity.
Abraham Lincoln did not believe in an afterlife (two of his sons died while he was alive) but he wrote a short document regarding God's viewpoint of the Civil War with which I am in agreement. In this document, Lincoln wrote: "God can not be for, and against the same thing at the same time."
If religions contradict one another (and they do) then logically speaking they cannot all be right.
Therefore, logically speaking, it necessarily follows that some religion is both of human origin and also contrary to the will of the Deity which we are postulating exists.
Now suppose for the sake of this discussion that my religion is not acceptable to this postulated Deity. Does that in any way defeat my conclusion that 99.9% of religion is false.
No, it simply would mean that my religious beliefs are among those which are delusional.
Take, as an example, the belief that Jesus is both deity and also deity's only spokesman since approximately the year 29 of the current common calendar. If that belief is wrong then all the religions that are built upon that fundamental belief are false and delusional. On the other hand, if it is true then all the religions which are not based on that belief are false and delusional. That belief cannot be both true and false. It must be one or the other.
Likewise, with all other points of religious belief.
What you don't seem to realize @cvdavis is that I do not believe that my belief in the doctrines in which I believe makes them right. They were either right before I believed in them or else I am deluded.
You asked how common my religion is.
One of my doctrinal beliefs is that in every age, the majority were wrong.
In the days of Noah, only 8 were saved from drowning.
In the days of Caleb and Joshua, they were the only two of the men who had been over the age of twenty when they left Egypt who entered the promised land because the majority were wrong.
In the days of Hezekiah when the Assyrians were destroying the majority of Israel because of wickedness, God promised to save a remnant.
After Cyrus the Persian defeated the Babylonian army only a minority returned to rebuild the temple.
And Jesus said "Enter by the narrow gate; for wide the gate and broad the way that leads to destruction, and there are many who go in by it. Because narrow the gate and difficult the way which leads to life, and there are few who find it."