Teaching on gratitude and& “duty” is not necessary for Nibbana. MN 117 states gratitude & duty is a defiled (asava) right view with attachment (upadhi) siding with merit. In MN 56, Upali's stream-entry resulted in independence from the teacher. In the Vakkali Sutta, Vakkali was rebuked for wrong gratitude. The Dhammapada 294 states to "kill the mother & father to attain Nibbana". In MN 86, the arahant Angulimala, ate his alms food without debt (obligation). Gratitude is a moral teaching for worldlings (puthujjana) but is unrelated to the goal of Buddhism, namely, Nibbana. Dhp 43 says:
Na taṃ mātā pitā kayirā, aññe vāpi ca ñātakā; sammāpaṇihitaṃ cittaṃ, seyyaso naṃ tato kare
Neither mother, father, nor any other relative can do greater good than the well-directed mind.