I don't know if you've tried this but when parrying thrusting weapons I like to sidestep the initial thrust and try to catch their drag, pointing down and to the left the same way you would parry a horizontal swinging weapon. I used to think longsword fights were boring m1 spam fests until I started using this method.
Thank god I'm not the only one who's having harpy troubles lately. I've found parries more consistent with them if you strafe and try to get the tip of the blade in the attack hitbox.
