I tried langchain agent and other abstractions and gave up after a few weeks. Things break randomly or after switching to a different LLm models (Claude vs Chat

I tried langchain agent and other abstractions and gave up after a few weeks. Things break randomly or after switching to a different LLm models (Claude vs ChatGPT). I determined that it was because of the prompt. So, I spent hours trying to make custom prompt. It works fine for me now but I wonder why I have to go through all that Frankenstein hack with Langchain and not just roll my own. I only use langchain for data loading now.