Ask HN: What are your thoughts on serverless function composition?

The serverless ecosystem is rapidly growing. There are several FaaS providers, such as Amazon Lambda, Azure Functions. But these are stateless. But our applications need state to function. So there are services like Step functions and Azure durable functions. What is your thoughts on them? Do you find them fulfilling or do they lack features? In a nutshell, what is that you expect from such services?