"Does this mean we are not training our young coaches to the best of their ability or are professional clubs bias and prefer foreigners or ex-players?"
You have a point but the cold hard fact is you are right and nothing will change that. Players will always have more success at the senior level, but there are exceptions, and americans will always feature heavily in our sport.
Phizzer AFL is played internationally - The USA for example has a semi-national afl comp. Do you think many Australian's are coaching in that league or americans?
If you are coaching kids because you want to coach professional basketball in Australia I would suggest go for it, but dont put all your eggs into that basket its unlikely, nae virtually impossible, you will coach in the NBL. Its unlikely you will get there. I think Aussies should seek to go over to US COlleges to coach. US people love AUssies, there are a lot more coaching roles over there (more schools/bigger coaching staffs), matters less if you played and its more money!