To illustrate my point, from my last game:
Defensive Anivia (me): 3K/3D/3A, 5 Caps -> 846 points
Roaming Trundle (ally): 11K/10D/9A, 1 Cap -> 871 points
Essentially this game was a 1v2 defensive stalemate in the bottom 2 towers between me and Udyr/Soraka while my team roamed to try and get other points. Trundle wasn't even assisting my allies in capturing points; he was roaming in the middle of the map just attacking people. I held 2 players off a node for 20 minutes, which I thought was pretty impressive, yet I was still the lowest player pointwise.
From the point system I have gathered the following: Killing randomly in the middle of the map and ignoring the control points is an equivalent effect on the game to defending.