It complex.
Power, ratio, style, types of fights he's fighting and how they end (even if nobody died).

Just an example:
You may have a certain maran with very high PK ratio who avoids to login when a lich is about but rather login when he can boost his ratio even further.
And you may have a player with similar skill and similar build who does otherwise. I believe you understand that fighting a lich is not the best way to build amazing PK count.
But both characters are somewhat equal in terms of overall game balance despite of their pk ratio being totally different.