Earlier quoted context omitted.
Consensual may not actually be given the power dynamics involved.
I am in no way in favor of staff-inmate relationships, but in most relationships the power dynamic is uneven. For example, in most marriages with children the breadwinner has significantly more power, but that does not make sex an assault.
Taking this charitably, I would agree with you that in general, sex might still be consensual even if there is some degree of subjective power imbalance between two people. rockstar-fan. politician-staffmember.
However, this does not mean that all power-imbalanced sex is consensual. teacher-underagestudent. undertaker-corpse.
(Strange things can happen when you mix up "there exists" and "for all"...)