The main reason ChatGPT took off was:
1) Response time of the API of that quality was 10x quicker than the Davinci-instruct-3 model that was released in summer 2022, making interaction more feasible with lower wait times and with concurrency
2) OpenAI strictly banned chat applications on the GPT API; even summarising with more than 150 tokens required your to submit a use case for review; I built an app around this in October 2022, got through the review, and it was then pointless as everybody could just use ChatGPT for the purposes of my apps new feature).
It was not possible for anybody to have just whacked the instruct models of GPT-3 into an interface for both the restrictions and latency issues that existed prior to ChatGPT. I agree with you on instruct vs ChatGPT and would further say the real innovation was entirely systematic, scaling and changing the interface. Instruct tuning was far more impactful than conversational model tuning because instruct enabled so many synthesizing use cases beyond the training data.