Fundamental mistake in the second section:
Without airports, airlines have no business. Without airlines, the airports have no business.
Without airlines, the airports still have a business. That's why they try to diversify so much so that they are not so heavily reliant on the fickle airline industry. If it all came to an end, the airports still have the land to develop.
only a literal handful of countries have ventured down the privatisation path
Yes, third world backwaters like the UK, Germany, The Netherlands, France, several other European countries, South Africa, Japan, the large South American airports, the large Indian airports etc. In fact most of the large airports in the world, with the exception of the US (where some are considering it, and almost all are run as for-profit businesses).