Very few people would call Christianity or Islam a cult

No, I think that's usually the point of the snarky definition of a cult as a "religion I disapprove of", i.e. Christianity and Islam have the same characteristics as organizations called cults, but are not called cults because they're popular.

"If you wake up tomorrow morning thinking that saying a few Latin words over your pancakes is going to turn them into the body of Elvis Presley, you have lost your mind. But if you think more or less the same thing about a cracker and the body of Jesus, you are just a Catholic."
-Sam Harris