Every coach is forced to put backups in starter position every year due to injuries etc--they all have to take "meaningful snaps" at some point. When in, they are paid to make plays. Backups have to play in the NFL every week--it's not coaching genius that makes them functional. It's skill, preparedness and necessity.
Wallace struggled his whole time here. He just had his best season in LV. Benford will be a backup to White. Jackson will go back to being a backup behind a second year player.
Look, he's a good coach. Getting "a lot out of a little" is fine and all, but getting the most out of your best players in the most important games is the metric that actually separates the HCs in this league, not coaching up benchwarmers.