One other thing to add is large-scale RLHF. Big Tech can pay literally hundreds of technically-sophisticated people throughout the world (e.g. college grads in developing countries) to improve LLM performance on all sorts of specific problems. It is not a viable way to get AGI, but it means your LLM can learn tons of useful tricks that real people might want, and helps avoid embarrassing "mix broken glass into your baby formula" mistakes. (Obviously it is not foolproof.)

I suspect GPT-4's "secret sauce" in terms of edging out competitors is that OpenAI is better about managing data contractors than the other folks. Of course it's a haze of NDAs to learn specifics, and clearly the contractors are severely underpaid compared to OpenAI employees/executives. But a lone genius with a platinum credit card can't create a new world-class LLM without help from others.