I suspect (but don't know) that a lot of religious people would be almost as upset at "most religious claims are false" as "your specific religious claims are false" even though, as you say, the former is almost a triviality. I also suspect that many would fall back on claims along the following lines: "Yes, superficially my beliefs and my Muslim neighbour's beliefs contradict one another. But we are fully agreed on the existence of God, and perhaps we are just seeing the same thing from different angles." -- and then they would not be willing to agree that most people's beliefs on religious topics are wrong.

I think I agree with you rather than Eliezer on the probability-of-God question, but the answer might well depend a lot on what range of possibilities we count as making "God exists" true.