You speak of RBs not being paid their value or worth. That is at the heart of the question. What is their value? According to who? In football they are paid according to whatever they can negotiate AFTER their first contract. You seem to say that RBs are to be valued in a different way than all other players or by legislation. This is what the rookie pay scale does....it legislates a value. it does not differentiate value according to contribution but rather by the speculation of this player's future worth based on when in the draft he is taken. This is something the players negotiated....they WANTED this....because vets saw it is a way to get a bigger piece of the pie for themselves. Now an identity group (RBs) is saying this should be different for them.
You speak of fairness. The CBA is the agreement to what is fair. Fair is entirely subjective. It was passed by the players, including RBs. It was agreed to by the owners. You can have personal issues with what they agreed to, but as with anything considering employer and employee it is a matter of compromise or it is with one-sided authoritarian rule. The formation of the Union itself thwarted what indeed had been authoritarian rule. Of course, we must also understand a couple of things: 1) no one is forced to play football for a living. 2) No football player is forced to be a RB.
RBs most definitely have a shorter period of productivity as a rule of thumb. Therefore, a smart team uses that period and moves on, not wanting to be tied to a long term contract when all the metrics say that it's usually a loser.
All choices in life have consequences. If one chooses to be a police officer there is a greater risk to life and limb than if one chooses to be a lawyer. If one chooses to be an airline pilot they have a largely disrupted family life in return for an enjoyable and profitable career. RBs have chosen a career position that can bring them the spotlight second only to the QB, and a very good living, but usually for a shorter period of time than players who chose other positions. These are choices that each much bear their own outcomes that will not be the same compared to their peers or to other professions.
If the Players Union decides that in the next contract they want to try to negotiate position by position, good luck. Because the first thing that will happen is that players will want a cap on QB pay that takes up so much of the teams' cap space, thereby depriving others of higher paychecks. Identity groups do NOT make for team players. Identity groups do NOT unite societies, they cause rupture to the greater society (or team). If the players want to create some kind of special rules for each identity group, they can try. But I doubt it will be the team owners who strongly dissent. The players will be at each others throats, just like our society is at each others throats as we break ourselves up into ever smaller identity groups.