Unfortunately I don’t agree with you. Different things have changed over time:

• For chatgpt 3.5 they moved to a “lighter” and faster (distilled) version, gpt-3.5-turbo. Distillation came with a performance price, particularly on advanced and less common cases.
• newer chatgpt-4 versions have likely been “lighten” for performance reasons
• context has been halved for chatgpt-4 on webui, meaning that the model forget more easily and can use half information to create text
• heavy control has been implemented on jailbreaking and hallucinations, that results in models less prone to follow complex instructions (limiting prompt engineering) and that prefer simplified answers than providing wrong ones (overall decreasing the chance of getting high quality answers).

All these changes have made working with gpt less pleasant, and more difficult for very advanced and specialized case, particularly with gpt-4 which at the beginning was particularly good.