The big benefit you feel from heavy fill isn't really from the extra weight. The extra stability comes from the fact that nothing is slipping around inside the bag. In the quest for "flowing" fill, the lost aspect was that flowing equals slippery. When you set your rifle down on a slippery filler there is always a little more room for it to slip around. That means your reticle will move with it. With a heavy fill, the weight of it and the tiny particle size doesn't leave room for any slippage because it's "preloaded"; all of the slippage has already happened when you set your rifle on it.
We went in the opposite direction of flowing fill. Our fill will move inside the bag but once it is pressured it locks together. It will give you the stability of heavy fill without the heavy. The weight is pretty much the same as a standard fill, maybe a few ounces heavier. But it is miles lighter than the heavy fill and just as stable.
https://precisionundergroundriflegear.com/product/purg-locking-bag-filler-preorder/