Great post, thanks for sharing. I wrote something similar a couple of years ago, showing just how simple it is to work with LLMs directly rather than through LangChain, adding tool use etc …

https://blog.scottlogic.com/2023/05/04/langchain-mini.html

It is of course quite out of date now as LLMs have native tool use APIs.

However, it proves a similar point to yours, in most applications 99% of the power is within the LLM. The rest is often just simple plumbing.