Yup exactly!! its a subtle change happening under the hood, When people have a good interaction with ChatGPT they attribute it to the LLM, but in most cases, its the agentic features in ChatGPT that wows you and not necessarily the smartness of the large language model.
Well there was is a lot of human element and infact this post was an output of conversations with different people talking about LLM and ChatGPT. I guess Claude over did the 'fix grammar and improve the language' instructions.
Sadly I don't have a Claude subscription for the number of tokens needed for Opus. Although I'd admit I used Sonnet to clean up and improve the language and grammar.