I would rate Emperor Kostyan as
50% imperial power
40% legacies and or tatoos
10% prep (aura/shield)

So if you take the codex he is fighting at 50%. And I am pretty sure most of his deaths outside of ganks will have come without the codex. Ofcourse with the level of expertise he must have reached by now his 50% will be more than 100% of many similar dagger specs.