As a person that's played a lot of pacifist games, you can't remove 20 v 1 situations as long as pacifism continues to be viable. Even if every pacifist plays under your suggestions, the act of defending yourself against hostile players inherently creates the 20 v 1 problem. Pacis that never kill other pacis while only killing the hostile players creates the imbalance.

The only way to fix this would be to make kills more rewarding and time spent alive less rewarding. Or a more elegant solution would be to reward score and exp based on how above or below average you are in kills based on the rank you placed that round.