ryogi's MEoDP looks much more developed than nanaya's. to see lines of death on something, the user has to understand the concept of death behind the object's existence. ryogi seems quite adept at that, being able to a cut a whole lot of things nanaya can't. she may even be able to cut liquids or gases or any abstract concepts such as spirits or spectral beings, as we see her destroy Fujou Kirie's apparition and the disease inside asagami fujino without physically harming her. a similar feat was performed by nanaya when he destroyed the vampire blood injected inside him by satsuki, but generally we only see him destroying objects with solid non-versatile concepts.
additionally, understanding the concept of death exerts a huge pressure on nanaya's brain. this trait is absent in ryogi, who can freely use her MEoDP without any drawbacks.
It is stated that otherwise, both MEoDP are functionally the same. but the anime version of Kara no Kyokai shows ryogi shiki seeing only the lines of death, not the points. the anime version of tsukihime shows nanaya/tohno shiki seeing both the lines and points of death. seeing the points is a major plot element in tsukihime. if ryogi cannot see the points, it will prove to be a major disadvantage for her.
in terms of combat style, ryogi shiki's fighting style is based on martial arts and techniques derived from training from an early age. the only traits she received from her family through birth are the multiple personalities. nanaya shiki only received little training with the nanayas before being taken by the tohnos, but his speed,strength, athletic and acrobatic abilities are obtained genetically and are heightened to the maximum capacity of human endurance, so they are bound to be greater than ryogi shiki's, who only achieved them through training. his assassinations techniques also seem hereditary, since it is unlikely that his time with the nanayas was sufficient enough for full-fledged training. the nanaya's assassination techniques seemed to incorporate as much head-on fighting as stealth, since it seems impossible to go against demons with only stealth as a weapon. this proves that nanaya shiki had enough fighting skill to match ryogi shiki on even grounds. his strength and speed also exceeded ryogi's but his fighting skill is based on pure instincts whereas ryogi's is based on pure techniques, skill and experience from training.
it is difficult to say which one will be the winner in a fight. without the MEoDP, it seems the edge given by ryogi shiki's superior fighting techniques will not be enough to cover the gap between nanaya shiki's already highly developed fighting skills augmented by superior strength and speed. but with the MEoDP, if ryogi shiki can see the points, she will be the clear winner against nanaya's limited use eyes.