Yes, backwards Islamic theocracies are a lot shittier than predominantly Christian but relatively secular and progressive western democracies. But I don't translate that into "Islam is more brutal than Christianity".

Religions make a big deal of seeing themselves as teams, and looking at the world as our religion is better -- or our God is stronger -- than the other guys. That's part of the psychology of religion, but it's not a good paradigm for understanding religion.

Religions also have a notion that there's a "true version" with each person thinking the other guys within their religion are getting it wrong. Again, part of the psychology of religion, but again not really how it works. The religion is actually subjective and people project whatever feels right to them onto their religion, which is also shaped by their culture.

As a rough analogy, I'd compare this question to asking what beer makes people the most violent, and taking as evidence the local beer they drink in some part of the world with lots of violence. It's not the brand of beer that's really determining whether you start picking fights when you get drunk.