In countries where police are armed I expect he would have been shot for not dropping the knife. Don't forget he wasn't just carrying a knife he refused to drop, he had already tried to murder 2 innocent people.
I think the police were incredibly brave and efficient in detaining him. He wouldn't drop the knife, he was a very clear danger. In that situation it's safer to subdue the armed criminal with booted feet than to try and use hands.
He deserves every bruise he got. In other countries he'd be dead.