Fundamentals are outdated - it's all based on old GPT-2/3 models which needed a lot of hand-holding and the whole point of chains was that those models were too dumb to run multi-task prompts, not to mention that by default some tasks are executed sequentially while they can be run in parallel, slowing everything down (see how they did NER).
They keep adding new models but it's a bolt-on on an underlying architecture based on old assumptions that no longer hold for LLMs with emergent abilities like GPT-3.5/4.
