'An excellent mage wasn't necessarily a powerful mage', but there was a second half to this statement: 'but if an excellent mage was perfectly prepared, then they were powerful'.
Without enough preparations, one mage would never attack the magical ritual of another mage.
Because a mage's power could be magnified exponentially with the support of a ritual.
Under normal circumstances, Field wouldn't necessarily be a match for Marche; after all, he had to flee while being pursued by just Brali and her lackeys.
Field's strength lies in the fact that as long as there existed someone that remembered and feared him, then he would not die; his other strength lies in his heightened sense of perception granted by his spirit sense. Both the human Field and Roger were people with powerful spirit senses, and it was thanks to this spirit sense that he managed to avoid being surrounded and caught by the enforcers several times.