I would be going with kirei with backup from command spells. He has legit physical feats with speed nearing that of a servant. And even though kuzuki used to be an assassin, I don't think he has the same level of experience and knowledge as of an accomplished executor of the church.
And Kuzuki only made saber trouble with ease because she really went easy on him seeing him as a normal human, and thus he landed some blows due to her being surprised. A servant having saber's level of melee would literally one shot the dude if not for holding back. So it says a lot about him but in the same time don't.
Not really. Kuzuki made trouble for Arturia because his Snake style is completely unexpected and it isn't predictable to the point where it's said that they are ''invisible''. In fact, Arturia was able to keep up with the first strikes only because of her instinct skill. Also, because Medea buffed him with magic which made his fist essentially be capable of denting her armor and etc.
Kirei does win, depending on what version of Kuzuki we're talking about here and the situation the battle is taking place in. If this is Kuzuki with buffs from Medea, Kirei wouldn't be able to avoid the first few strikes until he grasps how Kuzuki's Snake fighting style works and that would result in Kirei getting his skull smashed the moment Kuzuki's fist connects. If we are talking about Kuzuki with no buffs, Kirei would be able to take the first hits and would adjust himself to be able to fight back in the follow-up as he would know the fists move in a snake-like movement, which would essentially result in Kirei getting the upper-hand via Command Spell usage.
