most of these guys aren't edge rushers, QBs, corners, or OTs like you said are more valuable than RBs. almost all of them have higher cap hits than barkley does. some of them have injury histories that are worse than barkley (chubb, derwin james) and none of them have been as important to a super bowl winning team as barkley was last year (vea comes closest).
whether a highly paid running back is still with the team that drafted him is a distinction without a difference. good offenses put resources into running backs.
edit: also in a redraft scenario, the only thing that someone would care about is what production they are able to put on the field for the very next season and for how long they can maintain a similar level of production. how their career actually played out has nothing to do with anything.