I read enough old books to recognize nineteenth century political correctness when I see it (example: Enlightened Imperialism). It is markedly less obnoxious and omnipresent than twenty first century political correctness.

This could just be the nostalgia filter [...], i.e., there were also a lot of pure status signaling works back then, but they have since been forgotten.

Undoubtedly there were, but I think a fair assessment can be made by observing only people who were recognized as high-status intellectuals in their own day. When I look at books written a century or more ago by people for whom I know that they were recognized as such back then, I simply don't see anything like the uniformity of opinion among practically all people who enjoy similar status today.

Moreover, on many topics, it's impossible to find anything written by today's high-status intellectuals that isn't just awful cant with little or no value beyond signaling. (And it's not like I haven't looked for it.) At the same time, older literature on the same topics written by similarly prestigious people is also full of nonsense, but it's also easy to find works that are quite reasonable and matter-of-fact.

Even if my conclusions are somehow biased, I don't think they can be explained by a simple nostalgia filter.