In my opinion the Theravada tradition was developed to serve its purpose which is to cross over sentient beings who have affinity with the small vehicle doctrines. The Theravada tradition has produced countless of sages which validate its existence. The Mahayana tradition also produced countless of sages which also validate its existence.
The Hinayana Sages like the Arhats and Pratyekabuddhas do not understand Mahayana Sutras because they never planted the seeds to do so.
This is what competent Mahayana teachers do for their students. They help their students plant the seeds for them to certify to the Mahayana principles down the road. As you learn more about Buddhism, it’s called Literary Wisdom.
The Buddha taught Buddhist principles that are appropriate to the potential of the listeners. This is what makes him a Buddha. He knows exactly what you should be taught so as to help you progress on your path to liberation. As an analogy, you do not want to teach calculus to children, do you?
Ven. Ananda is in charge of collecting the Hinayana doctrines so as to teach those with Hinayana potential.
We teach Mahayana principles to all living beings because we want them to plant superior seeds of Buddhahood. We want the best for all of you. In fact, once you have planted Mahayana seeds, you tend not to be satisfied with anything less, when your spiritual needs arise.
By the way, we are not at all concerned with validating Mahayana or prove anything. Our objective is to help our believers end suffering and attain bliss. The better students will become Mahayana sages.
As to affinity, it varies from lifetime to lifetime. The more Mahayana blessings you have, the stronger you are attracted to the Mahayana teachings.
In particular, for living beings of this Dharma Ending Age, the Pure Land Dharma is by far the best suited method of practice because it can accommodate people from lowly inferior roots to vastly superior roots. It takes a lot of blessings to believe in Pure Land Buddhism. Now that you have encountered our Pure Land approach, I hope that you will continue to tune in and learn more in order to obtain rebirth to be with Amitabha at the end of this lifetime. There is nothing more worthwhile for you and loved ones than investing to be reborn to the Western Bliss Pure Land. Then your encountering our Pure Land Mahayana Dharma would have not been in vain.