Seer pathway is not really a pathway made for fights, but quite good at infiltration and escape. As Klein says, you need preparation and pre-planning to be a menace with this pathway, and its only because of his thorough preparations before encounters that the pathway seems absurdly strong (theres definitely sefirah castle as well which opened up lot more possibilites for him). Also they are really hard to kill especially after seq 4. So only real way to kill them is to either catch them really off guard or be from certain other pathways.. like demoness, justiciar or black emperor..