So Having kills represent your score is a bad idea. It encourages killwhoring and that turns it into deathmatch with teams instead of objective based gameplay.
I propose that a scoring system be implemented instead
each kill shall be worth 10 points,
each death shall be worth -10 points
in the case of a shared kill, points should be awarded according to % of the enemy's health drained (so that if A does 60% of the damage and B does 40%, A gets 6 point and B gets 4)
Destroying an enemy spawn shall be worth 20 points, and destroying an enemy om/rc shall be worth 50 (or part thereof)
Constructing buildings shall also be worth 10 points (or perhaps, different amounts of points for different buildings) at construction, and one point for each minute it stays alive.
If the building is deconned or destroyed, the points for construction are subtracted, but not the points for staying alive.
If a turret or tube is deconned or destroyed without doing a certain amount of damage (say 50 points), 10 points are subtracted.
Points shall also be awarded for repairing structures, say 1 point for every 5 HP repaired.
I'm sure that this setup needs some tweaking, but there's the prototype.