It wasn't their use as riflemen that caused them trouble, it was their lack of unit based tactics that slowed them. The man per man issue was never in doubt but Commonwealth doesn't do well with cross unit tactics and mission priority. There's a habit of freezing under fire when things are going "right". Though that is likely a cultural problem with their approach to war. I've heard the word "proper" way to many times in my life. However you are right about the Aussies, the Corps wasn't happy (understatement) about the assignment but they've been happily proven wrong.
Jinsei wa cho no yume, shi no tsubasa no bitodesu