I've been using LLMs pretty extensively in a professional capacity and with the proper grounding work it becomes very useful and reliable.
LLMs on their own is not the world changing tech, LLMs+grounding (what is now being called a Cognitive Architecture), that's the world changing tech. So while LLMs can be vulnerable to bullshitting, there is a lot of work around them that can qualitatively change their performance.
Essentially, you don't ask them to use their internal knowledge. In fact, you explicitly ask them not to. The technique is generally referred to as Retrieval Augmented Generation. You take the context/user input and you retrieve relevant information from the net/your DB/vector DB/whatever, and you give it to an LLM with how to transform this information (summarize, answer a question, etc).
So you try as much as you can to "ground" the LLM with knowledge that you trust, and to only use this information to perform the task.
So you get a system that can do a really good job at transforming the data you have into the right shape for the task(s) you need to perform, without requiring your LLM to act as a source of information, only a great data massager.