When I first heard the term ~20 years ago, there was speculation that we would use up the easily extracted oil, and it would just get more and more expensive to

When I first heard the term ~20 years ago, there was speculation that we would use up the easily extracted oil, and it would just get more and more expensive to produce as we were driven to more challenging sources, to the point that consumers would be driven to other energy sources. And so "Peak oil" referred to the peak of supply, as in the GP's usage. You are implying the peak will be whenever demand tops out, which technically would still be "peak oil" but not in the way it's been used for a couple of decades.