It really pains me to argue for it, as the yields from kills is my favourite mechanic.
And it is fine in the early ages - it's just that it scales so good in the later ages whereas the yields from tradion don't at all and the progress ones much less.
For example, a 20 city progress empire gets flat 60 science from their policy per turn. That's about one renaissance unit killed (marathon multiplier). And killing one unit per turn is a trivial thing if you fight against immortal civs in later ages.
Well, reducing it overall will hurt Authority a bit early, which will reduce snowball potential. Seems fair.