just read further, the OP person you were talking about is, getting weaker and weaker by plot goes by.
Just read that chapter when sumei fight that demon almost all of his attacks is useless to it and he just got all out on his magic power just to defeat a soldier general of an army. if you want it to go further, just read the novel, though just be prepared for a tons of non-sense filler and full of chuni explanations, but in short sumei is going in another way to deal with demons by playing tricks instead of firepower.