In short, an 8B model could degrade almost 10x after being finetuned on robotics tasks, while 500B model experiences a very minor degradation (~4%) and there's a hope that with a larger-sized model, it could become either zero or even negative (adding more experience improves general purpose reasoning).
What I am saying is that while GPT-4 could beat a finetuned GPT-3.5 class model, I predict good things about finetuned GPT-4 class models, when they become practical outside of OpenAI/Google.