I've only recently started reading the source material and I've learned that the Gnostics believe that the God in the Torah is actually an imperfect God (described as resembling a dragon) and not the true Father of everything. Jesus Christ's father is not the Torah God but the true Father of everything. Jesus Christ was trying to save humanity from the Torah God.
Seems pretty accurate to me. Many people say that jews worship the devil. Well, the Gnostics basically said the same thing in texts over 2000 years old. I've also heard the Torah God is a dragon bit before and thought it was a modern view. I didn't realize it literally was written in texts 2200 years old.
For example with Gnosticism, there seems to be an emphasis on hidden knowledge for salvation, but the Scripture teaches salvation by faith and works. So someone could "independently" conclude this is a wrong viewpoint (even if they didn't conclude Catholicism was true)
Likewise with Catholicism versus orthodoxy and protestantism, one might observe there were popes since the beginning of Christianity and that most groups typically have a singular leader. Hence one might tend to independently conclude that Catholicism has an edge on being historically consistent as well as pragmatic with having a singular leader.
And so on with other conflicting beliefs or heresies.