Honestly I'm happy to be proven wrong about the usefulness of it.
I've used langsmith and found it quite useful. I think I was just so jaded by my bad experience with Langchain, that I'm immediately skeptical of other "lang" products.
That being said, it's not doing that much. And you still end up having to use some of langchain's abstractions. If this current "make a cyclical graph of LLM agents that send messages to each other" thing has any staying power than I imagine we'll see a more robust option soon. Personally I'd love a way to build agent graphs in a strongly typed language with first class concurrency.
For our DSL (BAML https://github.com/BoundaryML/baml ) we found that adding a VSCode playground to visualize LLM function inputs and outputs was a massive win in terms of debuggability and testability, so I can see why langraph is going this way.