Here's my old belt rig. I think most of the bits are no longer available as-shown but the concepts still exist. It's state of the art circa 2008
Pistol mags and first AR mag are in rigid pouches. All reloads come primarily from the first AR pouch.
AR mags in 10-speed pouches are to backfill the rigid pouch. If there's nothing in that first pouch, the hand can just sweep back til it hits one of them. But they don't get "fed" under pressure. They're basically non-existent when empty so its possible to run entirely off the main pouch if wanted.
Partials get dumped in the dump pouch if you're trying to retain anything. A dump pouch is just all around handy for the line in a class as it can help keep you from needing to bend and pick as much. I've even tossed it on a regular belt for use during a pistol class when running from concealment. It's just handy, period.
Holster is on a really high-cut platform and rides more like a drop-offset comp holster than a drop leg. I've done a run-n-gun 5k in it so it's plenty good for any movement level i'm capable of achieving. But it also serves to keep the belt anchored at the right level and rotation. I've got an ALS now that has mostly replaced that older SLS.
I wouldn't move stuff to my chest until i'd exhausted options on my waist. It's just more comfortable there, and I think it's better setup specifically for rifle work. That said, it's not something i can toss on over my carry gear easily. I wouldn't fault any logic in tossing on a basic chest rig and ignoring belt stuff, if I'm practicing or training with a setup to mirror a "grab and go" setup that goes with my normal carry/dress. It wouldn't be hard to clip a mag pouch onto the belt similarly and still run reloads in the same spot.