Me dunno. Let's say he uses a 1000 mAh Turnigy Nano-tech 3S LiPo. The battery itself requires 77x35x17. Two 18650s require 65x36x18. So the main difference is 12mm or .2" of height. So we can say size-wise this is a relatively fair comparison.
Next, let's compare those
batteries in Watt-Hours. The Turnigy does 1000 mAh at 11.1 V, which is 11.1 Wh. My HG2s are 3000 mAh at 3.7 V, which in series is at 7.4 V and gives 22.2 Wh.
Now, one can argue that 18650s can't perform at 3000 mAH at their C-rating, which is true, but at the same time it's only about a 10~15% reduction, not 50%. Even if you assume a whopping 33% reduction, the dual 18650s still give 14.8 Wh.
Consequently, since I already have an sx350j Boxer that will last longer than a DNA200 version using a 1000 mAh LiPo, I don't see much need for it.