If I recall correctly, kesageri ("monk cut") is a diagonal slash cut, so named for hypothetically cutting along the line where a monk's jacket crosses diagonally in front (like keikogi). I don't see kesageri as a cut you'd use on armored opponents, given the location of the joint gaps between pieces of strapped-on armor.
In my obsevations, straight on vertical and horizontal cuts make more sense, not just in respect to where you would cut at the neck, shoulders, hip/waist, elbows and wrists, but also in the most efficient generation and dumping of power. A vertical drop cut contains huge power if the psoas (tanden) and femoral/kua-area muscles are drawn in and the body internally "drops" to bring the sword down. Even striking a helmet or face guard full on, the crushing force alone could bring an opponent down. Likewise, horizontal cuts using the power of winding from the femoral joints, waist, legs and feet, generate great cutting power. But diagonal "kesa" cuts seem, to me, to be kind of halfway neither here nor there in power generation, and almost seem to bleed it away, not as powerful as the other two directional cuts.
Guess I'll have to pull out the old bokkuto and test this again. Er, not on anyone, just an inanimate padded target.