I would expect that most players starting for an A-League title aspirant would be good enough (in terms of quality, setting aside ability to adapt to the style/culture/country/etc.) to play in the Championship.
The better domestic players have generally always been able to hold their own at Championship level, and even comparing the current Aussie crop over there (Meredith, Williams, Wright, Luongo, Irvine) to top domestic players in those positions (Lowry, Spira, Wilko, Grant, O’Neill, Antonis) it’s thereabouts.
A competitive side should have at least 2-3 such players plus 3-4 foreigners at that level or better.
If Brisbane wants to be competitive but is spending multiple foreign spots on League One/Two level players who’ve never even earnt a look in at Championship standard, then their ability to pick a diamond from the rough had better be spot on. Other teams are importing foreigners from Eredivisie, Bundesliga, La Liga.