I disagree with this statement, first, to a large extent, quality of life (QOL) is subjective and personal, what you may view as essential to improve your QOL maybe something that someone else does not view as having any impact on their QOL.
HAs and Cis are examples as there exist some deaf who do not view either or both as having any impact on their QOL and others who do so, there are many examples of this just on this board alone. It does not make one's view and/or decision right or wrong nor does the view held by one detract and/or add to someone else's view, it just is what it is: differing views on the same subject.
As for the second part of your statement, that however is factually incorrect first for many they will not have the same access to sounds if they do not utilize a HA or a CI. Again, there are many examples of posters who have CIs and who have stated that they can hear sounds with them that they could not with HAs and obviously, if they were unaided. Thus, it was physically not possible for them to do so without access to HAs or Cis. Second, if a person views access to sounds as important to improving their QOL then having HAs and/or CIs as opposed to not having them will have a direct impact on their QOL.
Rick