I’ve added additional articles on the history of issue firearm reliability:
The reliability of the AR-15 vs. the AK-47 designs are babbled about routinely. Here is the only factor that matters.
Any mechanism can break or become fouled to a point that it ceases to function. Kalashnikov’s famed design has a deserved reputation for reliability but it is just a gas-operated, self-loading small arm and it has more in common with the AR-15 than differences.
While certainly not definitive tests, these videos are enlightening:
AR-15: Mud Test
Vietnam Era M16: Mud Test
I guess not even the AK is flawless and the AR just might work under harsh conditions. Go figure!