You don't seem to understand the full extent of how powerful that actually is. Keeping an enemies SP reduced to 0 means that they cannot attack you by any other means than auto attacking.
The damage is also pretty impressive too.
What alot of the damage via HP/SP weapons do is they make your stats irrelevant, and it is more about how many times you can hit that other guy, it just does % of damage. More HP = they lose more HP per hit. Supposedly this worked well in Korea, though I have a gut reaction to it.
means sin with a fast attack could lock a caster down in a few seconds making them unable to get away.
And yes the KVM and BG will only have their effects vs players, with this update players are no longer "demi-human" they are a new "race" of players.
This means things like Hydra/thara etc needed to be updated to work on both demi human and player races (and they were) but KVM and BG were not. We can discuss this for a future patch, but looking at what the gears are for I think it makes sense to at least put them in PVP only items.