However, I kept wondering whether it is true. Let's assume that -by some miracle- all the bark people will suddenly become core people. That is, let's assume that everyone practicing ceremonies, superstitions, devotion, etc. suddenly arrives at a deep understanding of the teachings. Would that endanger the survival of Buddhism and the sangha? I doubt it. People would still build meditation halls; they would still give donations to the sangha and provide the monks with food; they would still ordain. All these actions make perfect pragmatic sense. Hence, I am not entirely sure about whether the sangha needs "bark" at all. But, let's do another thought experiment. Let's assume that -again by some miracle- all the bark people suddenly abandon Buddhism in favour of consumerism and materialism. In this case, the tree does indeed experience an existential crisis and it's survival is uncertain. The conclusion is that Buddhism depends simply on the total number of its supporters, rather than on its "bark".
First, it's just impossible that everyone has a deep understanding. It is always natural that only few people have deep understanding of their religion. That's why a religion can't survive for any long time or spread widely if it has only "core members with deep understanding" - because of this small number of its adherents. Very soon it will just die out. What is more, if everyone will only meditate and learn deep Dhamma, who will provide those meditators and scholars with everyday food and other needed things? Who will build and maintain monasteries, halls, kutis..? No one will - because to earn money for such support you have to work a lot and live normal lay life. And there must be *a lot* of such lay people to support at least one monastery. If everyone has deep understanding, who will choose to be a supporter instead of a practitioner? We calculated that here in Russia we generally need about 20 active supporters for 1 monk. So imagine that all of them are buddhists with deep understanding. Everyone wants to be a monk or a nun. Quite obvious, no one will be a supporter. Instead of this all 20 will go probably to Thailand to ordain there themsleves to live in a monkhood without any problems. Why? Because in Thailand there are a lot of highly religious people with blind beliefs and without a deep understanding, who are ready to spend money on monasteries and monks.
Just think about the situation in ancient India ~2500 years ago. Common people were very religious, as we know, and they blindly believed that supporting different ascetics, gurus, priests is good. This was that "bark" already, at that time when Buddha appeared in the world. If there were no such a bark, there would be no buddhism. Ancient Sangha could survive only because ancient indians generally supported all
"spiritual persons". The same attitude we can see now in Thailand - people believe in ceremonies, sacred amulets, in offerings and so on - and monks do this for them. That's why Thai Sangha lives on and you can be a monk in Thailand without any problems. Imagine the situation when all monks will declare that all ceremonies, pujas, amulets, blessings are empty and will stop doing this for thai lay people. Just give us your support, and we will lock ourselves in monasteries to learn deep Dhamma and to meditate. You will see how quickly buddhism will disappear. I heard the same situation was in India, when muslims attacked Nalanda University. Buddhist monks became "too scholastic", they were drown in the philosophy and were "too far apart from people". That's why when muslim armies stood near Nalanda, locals didn't even notified them about this danger. So thousands of monks were killed, tons of scriptures were burning for months. Buddhism disappeared in India.