I don’t think it’s presentism at all; indeed, I would argue my critiques would have been evident in the moment itself.
As for Astapor, it was absolutely Dany’s goal that there be a new regime in the city. We know this, because she went to the lengths of setting up a new government, “a council of former slaves led by a healer, a scholar, and a priest.” And we know that it certainly was not her desire to see that government overthrown, because we know the dismay with which she greets the news that Cleon has overthrown her government, reintroduced slavery, or started a new war with Yunkai.
I would argue that, at the very least, Dany’s advisers would have told her that no government can or ever has existed without a monopoly on violence, so that pulling every single trained soldier out of the city would leave the government unable to resist a coup.
As for “needing her troops there,” she wouldn’t have needed to leave that many soldiers in Astapor. Cleon didn’t have an army backing his coup, he was just a big dude with a meat cleaver and an angry crowd; leave the council fifty or a hundred.trained soldiers, and Astapor would still be a slavery-free, unsacked city right now.
As for “more importantly, none of them WANTED to stay” – assumes facts not in evidence.