Expendable denotes the idea that a position is plug and play and it doesn't matter who sits in the backfield.
That is not accurate as elite RBs make a huge impact on the offense as a whole.
The problem for elite RBs is not the impact they have while elite, its the limited window in which they are able to make that impact.
Normally an elite player, at a high impact position like RB, has the opportunity to earn a big payday for their first FA contract.
For RBs, since their prime is shortened by the nature of their position, have now lost the ability to get that 1 post rookie big contract that all other positions get.
No one is saying that any random ave RB should get paid more than they are worth, but it is obtuse not to realize that great young RBs are getting shafted