In general I would agree; a violent punishment (assuming you can manage one) generally does the trick for putting off physical bullies. However, they have workarounds, such as entirely replacing physical assaults with taunting, vandalism or theft (e.g. stealing books or puncturing bicycle tyres).

Teachers never notice vandalism or theft of pupils' property and since there's never any evidence they're not interested. If the victim responds to abuse with their fists then it can be reported to the teacher, who will believe the instigator of the verbal abuse. The abuser will have friends who will report that they heard nothing and the unprovoked attack caught them by surprise.

I wonder whether school children use smartphone apps to gather evidence these days (I left school before even mobile phones were common) and how teachers respond.