The death tolls are more tied to whichever empire happened to have a certain religion as its dominant religion as opposed to characteristics of the religion itself.

And then there’s the tricky bit of attribution. Were the crusades strictly driven by religion, or was it about control over trade routes? Is the British Empire a Christian Empire or was it more of a capitalist enterprise even if the head of state is also the head of the church? Was Mohammed driven by religious fervor when he started his conquests or was it imperialism? Was the genocide of the Rohingya done because of Buddhist teachings or because of a military junta trying to hold on to power? Do we start tallying the deaths by the Roman Empire under Christianity from 313 AD, or 323 AD? Can we just attribute what Israel is doing in Gaza to Judaism? Etc.

Honestly I wouldn’t even know which religion would be the most murderous if you looked at all of human history.