I think that most people at some moment in time see that the khandha’s are impermanent, changing, liable to arise and cease. Some moment in time we see that we are not in control too. We see, how our desire to be in control, and to have all according our wishes, makes us even feel more bad and only contributes to me misery. That is all part of commen sense, or common human experience, i believe.
We see and understand that clinging to the body, feelings etc as me, mine, my self , mind, existence is not helpful. Also this is common human experience. Many people who become ill see that there is no use in desiring for what once was, health, power etc.
I believe this basic life lessons we all make in life. We do not need a Buddha to let us understand all this. It is like life and suffering forces us to become more realistic and change our expactation, attitues, passions and views. Otherwise we only suffer more. Also therapist go this Path.
I believe many people do this. Maybe not as buddhist, but for humans it is normal to investigate suffering and its causes. We do not wish to suffer. Ofcourse we all know and see at any moment that our attitude, tendencies, wishes, desires, personality, views, identity, attachments plays a major role. We do not need a buddha to figure this all out.
Not always but still it is also quit common and natural that becoming older, one becomes more realistic and more dispassionate. It is quit normal that one day one stops feeding all those inner fires. It is natural for many people to take suffering as a lesson. This Dhamma, as it were, is not difficult to see and also one will do this is quit naturally.
But i do not believe that all these people who have had life and its suffering as a teacher and have not fed the demons, the inner floods, fires, are nobles. For me this is all to much common sense. To rational. For all this we do not need a Buddha, i feel.
I also do not think that we need a Buddha to know and see that emotions, thought etc are insubstantial. It is common human experience.
For me the uniqueness of Dhamma lies in asankhata, the knowlegde of that what has no characteristic to arise, cease and change in this very life. I believe that is what is really ignored or stays unknown or unseen by us. Anicca, dukkha and anatta are not really supra mundane. Such ideas are also common for worldlings, certaintly to some degree.