They weren't written down but they were chanted by groups of monks, and memorised like poetic sagas in Europe. The Buddha did not say 'few are able' but 'they bring no benefit'. This is the same point as made with the man pierced by an arrow and asking what wood it was made from etc: so is the monk who asks the nature of the self and the world. By pursuing 'gnosis' you do not understand their religion better than them, and are certainly not 'more of a Buddhist'. BTW, what do you mean by 'orthodox Buddhist': Theravada or Mahayana? Monk or lay? No, some don't realise and some disagree. And the Buddha went futher than the first noble truth: he saw the reason for the suffering, how it can be avoided and prescribed a cure.