So, here's a thing. It's somewhat rare for someone in an arena fight to get taken out by a single heavy attack in isolation or attrition by lots of such attacks. Generally, you have to force the opponent into a bad position where they've got no real good options before you land any meaningful hits. If the attacker and defender are both fully at the ready, any isolated exchanges will generally end up close to null. 

After launching a swing that my opponent parries, I typically play off of that position to try force the enemy into a bad spot. For example, in an unarmed fight, I might take a hand from a punch that the opponent parried, thus right next to the opponent's arm, and attempt to grab the parrying arm. Then I might pull him in and off balance so that I can strike with the other hand.

It's certainly possible to win by a single heavy attack in isolation or attrition, but it usually only happens when the fighters are very asymmetrical or one of them pulls off a very clever trick.