from the way i see him, he has a normal growth rate of regular person however his entire squad is full of cheat like people. so basically he thinks that he is weak because he is comparing himself to them but in reality he is still a strong person, like at least S rank while the rest are SSS ranked. he feels like an Aux Mage than a main vanguard combatant too from the way he hoards artefacts, so he really downs his own abilities without knowing he is not exactly weak. normally even disciples would scorn their masters if they are weak but since she knows his abilities, she respects him because she knows what he is capable of. plus he is calling the quest easy after reading it multiple times while she is still scared of dying from the quest given to her that she wants to write a will...