Have you ever read any classical period histories?
Anything by the Persian Empire, the Assyrian Empire, etc., the Peloponnesian Wars, Carthage, The Mithrandatic Wars, The Galic Wars, and the Wu Hu in China. These were genocides/gendercides that had religious elements and were situations where all where non-monotheistic powers. Think about the Egyptian empires.
And that's just genocides. Polythestic tolerance is mostly a noble savage style myth.
I dont believe it to be an outrageous statement that late polytheistic roman empire was more tolerant than early christian monotheistic roman empire.
As a parallel commenter noted however, the level of official tolerance varied by era, who was in charge and where. Another parallel commenter noted that the rituals of the official roman religion were considered ritual first, and religion second.
The goalposts have moved a lot from the original argument, but the only way that you can make an argument about tolerance within the historical record is simply by ignoring intolerance to Jews, Persians, Christians (generally all non-Italians) and the various barbarians that Rome contended with.
In fact, the intolerance of Germans and migrants, in particular, by both "pagan" and "Christian" (neither label really fits), was a key reason for the eventual fall of the empire. That was not necessarily religious, but arguing that the martyrdom period, as well as the German wars, were somehow more religiously tolerant the late empire, is ... dubious in my point of view.
You can make arguments that the Middle Ages crusading church (i.e., the Catholic Christendom church 500 years later) was less tolerant, but few things in the Middle or late Roman empire (or anywhere in the world) could ever be described as tolerant.
Being intolerant of an insurgent monotheistic faith doesn't mean that it was not broadly tolerant of other faiths.