The Overton window is not purely defined by what the audience thinks. Consider the Soviet Union, Nazi Germany or the US during WW2 when freedom of speech was at best a farce. In quasi democratic societies you’re constrained to stay within some distance of the median voter or have any attempt to influence the discourse break down. That’s plenty to influence politics. There’s a lot of difference between +1 and -1 standard deviations from the mean in politics, plenty to sustain the tribalism that’s the driver of most politics. Maybe you need to go up to + or - 2 s.d. to dampen dissent but I doubt you need to go further.

Imagine if the internet didn’t exist. Do you think anyone would have payed attention to the German New Year’s Eve rapes? It’s not like anyone in the media class was going to do it before the cover up was a story in itself.