A level 10 bolt setup will only be lighter under certain circumstances. If you go with a really stiff spring and aren't using the optimum barrel length the increase in chamber pressure and resulting force on the on-off pin more than offsets any decrease in friction force due to the sear interacting with the bolt. This results in the level 10 having a heavier trigger pull. However, if you utilize a setup that keeps the chamber pressure lower, then the lower forward force of the level 10 bolt will result in lower friction and the increase in force on the on-off pin isn't as dramatic so the overall result is a reduced trigger pull force.
If you measure the trigger pull force on a mag, and then measure the force required to push the on-off pin without the bolt installed, you will find that there isn't as much differece as you would expect. This would indicate that most of the force is actually caused by the on-off pin and not the friction of the sear on the bolt.
The efficiency of both bolt setups depends heavily on the barrel length used. Each has a different optimum value. You can't compare efficiency unless you find that optimum value. For most user setups, I think that the level 10 bolt causes the barrel length to fall farther away from the optimum length value, which is why most users experience reduced efficiency. That inefficiency is a direct result of how the level 10 dumps air compared to the level 7. Using that information, the idea for using inserts in the chamber was tried and was actually found to provide better efficiency.
Except for the Automag in front, its usually the man behind the equipment that counts.