At 700 AD the Zoroastrians are well into the process of being subjugated by various Islamic faiths, so a colony in Australia is practically nil. Even if they knew about Australia, there would be no reason to go there since it offers very little compared to settling in India.
Australia is not a very hospitable place, especially not the only part of the continent known for centuries, Western Australia, with its deserts and savannas. Agriculture is barely possible in that environment, so the population would remain small.
Also, "reluctant to accept assimilated people", what is that supposed to mean? I'm pretty sure assimilating people isn't related in the slightest to any nation's success on the global stage, except for maybe post-colonial nations like the United States. This country would have nothing to do with nations like the US or Canada or OTL Australia. And I'm also pretty sure that Zoroastrians could and did assimilate other groups, given Persia's history. A lot of Persian culture later carried over to Islam and assimilated other groups (i.e. Turks) too.
Zoroastrians have no inherent business acumen. Parsi culture has encouraged that, but that's more because of their centuries long status as a minority group (akin to the Jews or Chinese in Southeast Asia). These are not Parsis, these are a different group of people. It doesn't make sense they could ever have a population the size of the United States (Australia physically cannot support that many people without futuristic solutions) or conquer large parts of the world (being right next door to those countries, they'll have similar technology, organisation, etc.). And I don't see how Zoroastrianism being a "rational faith" (whatever that means) somehow means "more science".