The segment gave an impression that it's a narrative that had largely fallen by the wayside by the early 1990s before it was revived again by the PRC government to deflect criticism after the Tiananmen Square incident.

You're referring to Evan Osnos' segment. I only just listened to it myself. He's not wrong.

Basically, at the time that the era of "National Humiliation" came about (the titular Opium Wars), the country really wasn't much focused on the foreigners. There were much bigger problems facing China than British gunboats, it was felt by the Court. It really wasn't until the beginnings of the Anti-Imperialism movements that lead to and spread past the May Fourth period that the notion of this humiliation became clear.

During that period, more often than not it wasn't the Westerners that were blamed most vocally, but corrupt officials, poor management at home, and a national culture that had fallen behind. The idea at the time among Chinese was that their own culture had been backwards and stagnant, that of course the Westerners had overpowered them because as a nation, the Westerners were stronger. This was the prevailing attitude in a time when the ideas of Social Darwinism were very much in vogue.

At any rate, this interpretation didn't last, and by the time the Communist Party was developing, the focus of blame was starting to shift. While people certainly had shifting opinions, the shift was also a useful tool for the political parties. It was on the basis of this narrative of the Century of Humiliation that the CCP was able to claim legitimacy. The humiliation at the hands of Western (and Japanese) imperialists was an important feature of the founding mythology of the People's Republic on the tails of May Fourth. It was also an important part of the narrative of the KMT, with both parties claiming credit for ending extraterritoriality in China in 1943 with the signing of long-named treaties between China and the US and then China and Britain.

While the continued push of this narrative died down in intensity in the lead up to 1989, the point made in the podcast about its resurgence after the crackdown at Tian'anmen is accurate. There was a clear and planned resurgence of the narrative immediately after Tian'anmen.

Quoting from Béja (2011):

Since 1989, emphasis has been placed on ‘patriotic education’ that develops the discourse of the humiliation of China by Western powers, and states that the Communist Party has saved the motherland.

And from Bonnin (2011):

During an important working meeting on propaganda held in early 1994, Jiang Zemin stated, ‘The international community is resolutely opposed to China becoming strong and powerful and will never abandon its stratagems for Westernising and dismantling China.’ He added, ‘In China patriotic, collectivist, and socialist education are one and the same thing. They are mutually supportive.’ It was around this time that history textbooks and museums systematically produced references to the ‘national humiliation’ to which China was subjected by the Western powers during the nineteenth and twentieth centuries.

And Quoting from Cabestan (2011), this and the above two all being found in the same volume, The Impact of China’s 1989 Tiananmen Massacre.

After Tiananmen, China was diplomatically isolated. Most Western countries froze high-level contacts with the Beijing authorities for around two years. … In the aftermath of these political earthquakes, the CCP … gave priority to consolidating its grip on China’s economy and society. To that end, at the instigation of Deng Xiaoping himself, it intensified its nationalist propaganda, turning nationalism into a core substitute for Marxism-Leninism, and restored the CCP discourse on ‘national humiliation’.

The point is that, Osnos is not presenting a controversial opinion here. It's well backed in the historical record. The machinations of the party's efforts to contain attitudes at the time is well documented and clearly reflected in the shifts in curriculum that happened in the years following the events of 1989.

References:

• Béja, Jean-Philippe (2011) 4 June 1989: a watershed in Chinese contemporary history (Introduction) in Béja, Jean-Philippe (ed.) The Impact of China’s 1989 Tiananmen Massacre. Taylor & Francis.

• Bonnin, Michel (2011) The Chinese Communist Party and 4 June 1989 in Béja, Jean-Philippe (ed.) The Impact of China’s 1989 Tiananmen Massacre. Taylor & Francis.

• Cabestan, Jean-Pierre (2011) How China managed to de-isolate itself on the international stage and re-engage the world after Tiananmen in Béja, Jean-Philippe (ed.) The Impact of China’s 1989 Tiananmen Massacre. Taylor & Francis.

See also:

• Kaufman, Alison (2010) The 'Century of Humiliation,' Then and Now: Changing Chinese Perceptions Of the International Order, Pacific Forums 25:1

• Wang, Dong (2003) The Discourse of Unequal Treaties in Modern China, Pacific Affairs 76:3

(edit: formatting)