Langchain don't support basic things, like splitting a list result in single items and processing those one by one, accumulating the results further down the road.
By the time you have built custom chains, custom prompts, and custom agents to support all that, you basically are using their interface and not their code. At that point, eh, it's pointless. It's great for demos, I give you that, but every time I tried to coherce it into a product, it fell short.
Some prefer React, somet NextJS. LangChain has its place.