So your character has an instant cast shield that blocks incoming attacks regardless of their power? Seems a bit overpowered, to be honest. Your characters are supposed to be of similar tier level, so when working with something as subjective and unbound by logic as 'magikz' the prep system is, as I've already said, a way of balancing combat without the need for dice rolls or coin flips. Sure there's a place for strategy and logic, but if you follow what is logical to its logical conclusion, combat at higher tiers is incredibly pointless. What would be logical is using your immense magikz to just displace half your opponent's body, to instantly remove their heart or their brain and render them inoperable. No one does that though because it wouldn't be a RP fite anymoar, but it is the most logical thing to do. 

See what I mean here? If you take logic too far this stops being a game, which is what RP is. Imagine if someone walked into a chess match and said 'well, these rules are good and they work and all, but I can create a real compelling argument for why I should be able to move twice in a turn.'

Would that make chess better? Are people who request you follow the rules in chess Templars, or ISIS members? By the way, that is genuinely a horrible analogy. 

Also you really shouldn't need the prep advantage. You have an almost unlimited variety of spells to work with, perfect for ambushing. Corban is really forced on the defensive and to react to whatever you do in this fight. People using guns or swords rarely utilize the prep system, and they still eventually score hits. You just have to attack in a fashion that leaves your opponent out of options, physical or magical.