I have no idea what you mean by victors' "tall tales" created to "demonize [...] enemies" in this context, but as for the rest:
I strongly disagree. It is not one bit less "impressive" to stand up against oppressive tyranny because one has been personally victimized by it (rather than merely because it offends one's ideological or philosophical abstractions). Quite the opposite, in fact. How else was there to be a Spartacus if Spartacus had not first been a slave ... ?
And the willing defiance of erstwhile idolators is made even more impressive by the fact that the still-faithful - especially those among the power-wielding priesthood - hate apostates even more than they hate the heathens who were never believers to begin with ...