You need to be international to succeed in the 21st century.
That hasn't seemed to help the A League much at all. Simply existing doesn't necessarily mean succeeding, just as expanding doesn't mean it either. Let's just wait and see if the new Sydney and Melbourne clubs not to mention Gold Coast and Nth QLD clubs are around in 5 years time to see if they'll be a success or not. I'd be willing to bet plenty that at least one and likely more won't be.
Soccer might be the self professed "world game" but it's that very international popularity that you claim is needed to succeed in this country that's the very reason why the A-League has been and always will be the little brother in regards to where it sits in the pecking order of the big competitions the NRL, AFL and even Onion. Out of the 4 competitions,
if one of them were to fold i don't think there's any doubt it'll be the A-League and that's even with the international popularity is enjoys. I'm sure soccer fans will disagree with that but it's hard to make a strong argument to say they'd survive before the other comps.
We might lose some players to the UK to play league but the best of the best stay here which means we'll always have a very strong comp and will always have a strong supporter base. The reason why you think AFL won't succeed (because it's not international) Is exactly the reason it will always thrive in this country even with the major interest only in 3 states, they won't lose any players overseas so they too will always have the best of the best to keep their comp strong. Can the A-league say the same? of course not because the vast majority of the best players who can cut it overseas will follow the money overseas (rightly so) which will continue to make it just a mediocre league.