While disagreement is often violent, I think if you look closely most of these disagreements are actually politically motivated rather than reflecting deep divisions in core beliefs. Prior to the advent of nationalism this was simply a good way to rally the troops for whichever geopolitical objective.

In terms of core beliefs, I think your estimate is rather low. Obviously it depends on how you weight it, but the core beliefs of the Abrahamic relgions and even Hinudism and Buddhism have a lot in common.

> At the very least N-1 of N religions are wrong

I will take it further than this: 100% of all beliefs are at least partially wrong. Ultimately, one has to ascribe weight to something.