Many of the recommended waist packs look nice Aaron, but if you try to load them with 4.4 lbs of water (2 liters) and a pound or two of other gear, misery will ensue in short order.
The good ones don’t do that.
MountainSmith’s, for example, ride like a backpack — just with optional shoulder straps. That’s because the belts are essentially identical to a backpack belt. I routinely carry 20 lbs (10 kg) in mine, without noticing it.
Similarly, my old North Face fanny pack holds about 10L and rides just fine. It, too, has a nice wide belt. It does work better with short, wide, bottles shaped like Nalgenes rather than tall SmartWater bottles.
Military LBE (Load Bearing Equipment) belts/harnesses are designed to carry much heavier stuff than water.
Dan Timmerman (Timmermade) runs with his belt packs.
Flimsy packs on narrow belts roll and flop and don’t work well, exactly as you describe. Tall bottles are better on shoulders due to their length (and the ability to connect at top and bottom).
The clips that I showed in my first post don’t flop at all, because they are attached at the top. For running/scrambling, it’s easy to add a loop or pocket at the bottom, as I said.
Like your OMM belt, the good ones don’t tend to be featherweight. If you don’t suspend (or balance) the weight from the top, then the pack needs to be stiff.
But well-designed lumbar packs are just that: well-designed.