Or is that camera too heavy for the rig?

The answer is both. It works but it's heavy. But you can create good looking and stable shots with a little patience and muscle.

Dude, I tried out a Fig Rig at NAB with just a little camera on it (what's the Sony HDV camera smaller than the Z1/Fx1?), anyway, it is very uncomfortable weight distribution and was quite a workout with a 4 lb camera. A decked out JVC can easily run over 13 lbs. I don't think its practical (check out the latest DV magazine where they review it and agree its not great weight distribution).