It appears this hypothesis has come true with GPT-3 and the new API.
On a fundamental level, I agree. However, there is some aspects of this technology that makes me wonder if things might not be a tad bit different and past experiences may not accurately predict the future. Artificial intelligence is a different beast from what we are used to, that is to say "mechanical effort".
When it comes to multimedia deepfakes, the threat is less "people believe everything they see" and more "people no longer trust anything they see". The reason why we trust written text and photographs is because most of us have never dealt with faked letters and most altered photos are very obviously altered. What's more, there are consequences for doing so. When I was a child, I sometimes had my senile grandmother write letters detailing why I was "sick" and couldn't come to school or had her sign homework under my father's name. Eventually, the teachers found out and stopped trusting any letter I brought in, even if they were legitimately from my father.
Great takes on all this, better than a typical reply.