Definitely not inevitable. Most of the population growth is immigration from places that have no interest in AFL - Asia, UK, middle East and Africa. Soccer is the winner there.I get what you’re saying but as Sydney’s population keeps growing, both clubs are eventually going to get bigger crowds and more members, it’s inevitable.
The only way they won’t is if they put more teams in Sydney. Sydney isn’t Melbourne, and even some Melbourne clubs struggle to get good crowds i.e. Dogs v Port game, most Norf games.
If they stick with two Sydney teams, they should be fine long term. Developing a local rivalry is a good idea.
As for Gold Coast, it’s one team in a market all to itself. There’s only upside. In time, they should check out okay, it’s the lack of success on field that has ****ed Gold Coast sporting codes in the past.
I do agree about Tasmania. For too long they have been denied, as were Canberra in the 80s and 90s too, I believe.