An explanation can be reasonable while the arrangement remains unfair.

Good reasons and fair outcomes are separate things, and they come apart more often than we admit. Every step in how something was decided can make sense, and the result can still leave one person carrying far more than the others. Being given a coherent account is not the same as being treated well. You can nod along to the reasoning and remain right about the unfairness.

If you have accepted something because the explanation was hard to argue with, look again at the arrangement itself. Ask what shape it has, not how it came about. You can say the reasons are sound and the split still needs changing.