"Dath ilan actually doesn't sound ahead of, say, Absalom on tolerance of dissent to me. There are no things I'll be arrested for shouting in a public square in Absalom, and a lot of things I would be arrested for shouting in a public square in dath ilan. There are no books that I will be prevented from writing and distributing in Absalom, and a lot of books I'd be prevented from writing and distributing in dath ilan. Absalom does not violently suppress Rovagug cultists. Osirion wouldn't suppress people who were just trying to have lots of children who'd agree with them the universe should be destroyed and not actually planning the actual release of actual Rovagug. It wouldn't negotiate with them because there'd be nothing to negotiate because they could under our laws just go living their lives as long as they weren't actually trying to do a violent crime.
You just said 'If the gods are real then, yes, you'd want to remove all works of fiction that would let somebody contact them. This also seems like a totally reasonable thing to do' and that is a degree of social control that no Golarion society except perhaps Nidal attains. Rahadoum bans all the gods and all their followers, but they don't ban works of fiction in which the gods are described.
In many respects dath ilan sounds lovely. I have conceded that perhaps the degrees to which it is an unusually oppressive tyranny heard of is in fact better than many other possible ways it could be - for example, if you do have a problem with aliens sending you mind-viruses. But I am not redefining anything, when I name it an unusually oppressive tyranny with unusually little tolerance of dissent."