I think the "minor" or "less important" perspective comes from Sinologists, or at any rate people who are thinking more about China than about the Abbasids, much less the Zoroastrian elite of the region. After all, even if the Tang had defeated the Abbasids, Chinese forces there were very far from their centers of power, really at the edge of even nominal Chinese control at practically any pre-modern time, so they couldn't possibly create a very strong presence there. From the perspective of Xi'an, a victory at Talas, by itself, would mean a few years, maybe decades, of nominal suzerainty over faraway princes, then too many problems at home and on the supply lines to those peripheral garrisons would show up to hold on to even that bare pretense of power.
Assuming that the Abbasids still have any influence and control in the region at all, that right there would be a perfect opportunity for them to come in and snap up those Zoroastrian princes you mention (or for ambitious Persian Muslims, etc.). That would certainly lead to changes, but the significance is hard to assess...