That compares ChatGPT to mechanical turk, not to a smaller, more specialized model. Mechanical Turk is just crowdsourcing.
You can also probably distill a large model to a smaller one while maintaining a lot of performance. DistillBert is almost as good as Bert at a fraction of the inference cost.
GPT-3.5 and 4 also currently aren’t deterministic even with temperature zero, which is a nightmare for debugging.
What's definitely true is that getting decent data often takes some care, especially in how you define the task. And mechanical turk is often especially tricky to use well.