There are multiple ways of being open. Open as in open source, and open as in you can already play with GPT-4 while Google keeps people waiting for PaLM. There's also open like the LLaMA "release". If the model is not excellent (see BLOOM) it doesn't really matter it is open.

You can be sure that the API-only access to GPT3 had a major impact on AI in the last 2 years - what projects people worked on, what studies were being made. Even dataset construction for other models. GPT-3 is an excellent data labeller.