I agree 100%, the problem is the heavier bb carries its energy farther. If a gun fires a 0.25g bb at 3.52j muzzle energy, and another fires a 0.43g bb at 3.52j muzzle energy they will both hurt the same at the muzzle. At 100 feet it is a much different result.From every ounce of physics intuition I have, I have to say the heavier BB being more dangerous on impact is crap; given the same surface area, X-Joules is always X-Joules, a 0.20 at X-Joules is just as stingy as an 0.40 at X-Joules.
To combat this as a field owner/event organizer you simply need to chrono the airsoft gun with the bb weight the player will use.
You also have to set the MED for the bb weight.
An airsoft sniper with a 3.52j muzzle energy will have an MED of 70 feet (21 meters) at my local field, but the same gun using 0.43g bb's and a muzzle energy of 3.52j would have an MED of 115 feet (35 meters).
The heavier bb carries its energy farther. It also is slower to accelerate and has a longer time in the bore under pressure.
So chrono with what you use, set the limit by joules at the muzzle, and set the MED by the bb weight and muzzle energy.