They signed Jones on what they hope he becomes. If he doesn’t take a step forward he’ll be replaced. Yes his production can be replaced easily. That is the thin line with QBs. Coaches and GMs get fired over these decisions. We all know why teams take the risk.
Barkley is an elite talent at RB. He’s one of the few deserving of a top RB contract. His issue isn’t so much about being replaceable, it’s injuries. If Barkley were durable he would’ve reset the RB market. There’s so much working against RBs. The elite ones also have to be durable which is hard to do.
The main issue for RBs though is the committee approach which gives opportunities to lesser RBs. These lesser RBs then show they can do the job cheaper. Most teams use 2-3 RBs consistently.