"Dividing Points" among cheating students
To add to the existing arguments:

The punishment for cheating should always be higher than the direct advantage gained from it. For example, if somebody cheats at one task in an exam, the penalty should not only be failing that task but at least the whole exam, if not much higher. The reason for this is simply that you cannot possibly detect all attempts at cheating and thus the punishment should aim at being sufficciently high to make the average outcome of cheating negative if the detection rate is taken into account.

Of course, it is quite difficult to even estimate the detection rates for cheating and thus to adjust the punishment accordingly, but the punishment you are describing is certainly too low.

This aspect is not only important for discouraging cheating, but also from an ethical point of view, as cheating should not yield an advantage over the honest student.