I was inclined towards A , as I feel that a more powerful spell should be harder to dispel and a more powerful amge can always write a more complciated version of a spell
Entering houserule territory, yes...
New Mastery option: Gordian Knot ? Adds Mastery Score x 5 to spell level for dispelling purposes? Or perhaps doubles it?
(Cheap way for combat magi to become more effective against other magi, however, which may or may not be a problem)