So when an employee shunts a task off onto a coworker abusing their agreeableness, you're saying that other coworker deserves it and that the first employee is morally justified because they haven't "put in the energy" to be assertive in a hostile working relationship?
Almost any request can be framed as abuse in this manner. "Some stranger asked me to stand still on the street the whole day, he abused my agreeableness".
Imo it is not abuse if there isn't any threat and you simply can say no. If you keep saying yes to everything you coworkers ask from you, what do you expect is going to happen? It is your own responsibility to not be a doormat, that is abusing yourself.
One answer: You are responsible for your agreeableness. Your agreeableness is an OFFER to the people around you. Stop making offers that you resent honoring.
Another equally valid answer: If I care about you, and to the degree I care about you, I willingly modify my behavior to help you live better and more happily, regardless of the how you may deserve or not deserve it.
My wife is one of those people who will work themselves to the point of collapse without complaining. I have to be careful what I ask for because she will assign herself secret tasks to provide it. I don’t lecture her on how she deserves her misery, I remind her that I am the only person around here who swore an oath to help her, and she should ask me for what she wants and expect me to provide it. Then I try to volunteer when I see her working at something I can do. And I try to make myself easy to approach. After 32 years we have a pretty good understanding— but her endurance is worsening over time and so there are new challenges.
