A kettlebell swing should not be a squat. If the kettlebell travels below the knees during the exercise then you're squatting your kettlebell swing and putting too much pressure on the lower back instead of using the glutes.
To correct this, stay upright a lot longer than you think before you start hinging (or bending) at the hips. One way to get yourself to hinge back is to imagine the movement you'd make if you were kicked in the junk. Your hips are going to hinge back violently – you're not going to do a squat.
A cadre of coaches discuss various bodybuilding and powerlifting topics, including the wisdom of trying to build size and strength at the same time, and the relative benefits of isolation movements vs. compound movements.