Well said. It is possible to be a supportive validating counselling partner within a Dominant role, and while everyone is different, someone who is having restimulation flashes in sub mode is probably best kept there to work on it as a task for hir Dom. After all, you're a sub because you feel safe and supported under someone else's control.
And no, I don't think it is an unfair responsibility. Unexpected, maybe, but that's why this thread is valuable: to let other Dom(me)s know that this may be part of the responsibility they're taking on.