Using metaphors is dangerous, but I would dare to say that big tech AI is like cement suppliers. It's too low level of a service. In civil engineering you have the option to contract value added suppliers that will give you prefabricated pieces in concrete or steel you could be using to build your construction.

I'm seeing a lot of AI firms building value added services on top of big tech "foundational" AI offerings. Value addition can start very early at a clear plans/billing structure, going through rate limiting, documentation and extra features that will bring stability or consistency to our AI enhanced products.

Going the other way around (I tried) and building things on top of big tech AI is challenging starting at the fundamentals as the OP described well.